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Author's purpose and perspective — ACT practice questions

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What this topic is

Author's purpose and perspective questions ask why a writer includes something, and the stems often end with primarily serves to.

The answer is a function, such as introducing a counterargument, qualifying an earlier claim, or giving an example, rather than a summary of content. A passage's main purpose works the same way at full scale. Perspective concerns where the author stands, whether neutral, enthusiastic or doubtful, and it shows in which points get emphasis.

Choices begin with verbs like explain, argue, describe or criticize, and the verb matters: a passage that explains a process is not necessarily arguing for it.

Sample questions

Pick an answer to see whether it is right — nothing is saved, and nothing needs an account.

Passage A

NATURAL SCIENCE: Passage A and Passage B both address the topic of “Heat on the Rocks.”

At low tide, the black turban snails in
Graystone Cove seem motionless. The
receding water leaves a dark band of
rock that can bake within an hour.
5
Look longer, however, and faint
trails appear through the film of
algae. The snails move into cracks,
beneath sea lettuce, or onto exposed
ridges. A few pause at the wet edge of
10
a pool; others climb a few centimeters
and stop. My research asks whether
these small movements help them
manage heat.
The question is not idle. Intertidal
15
animals cannot retreat inland, and a
summer low tide can last long enough
for rock surfaces to exceed
temperatures that damage tissue. If a
snail’s path through the cove is a
20
form of thermoregulation, then maps of
movement should line up with maps of
heat. If the paths are merely feeding
routes, the temperature record should
look more random.
25
Our team marked 180 snails with tiny
numbered dots of nontoxic paint. We
divided the cove into three zones:
shaded crevices, flat open rock, and
ridges cooled by frequent spray.
30
Every fifteen minutes during six
daytime low tides, we recorded each
visible snail’s location and measured
the exterior temperature of its shell
with an infrared sensor. We also
35
placed empty shells in the same zones
and measured their exterior temperatures
at the same intervals with the same
infrared sensors, allowing us to
compare heat due to location alone
40
with temperatures of occupied shells.
Because the empty shells could not
crawl, withdraw, or wet their feet,
they served as physical models of
place.
45
The open rock became hottest,
sometimes reaching 38 degrees Celsius.
Snails initially found there were
increasingly likely to move toward
crevices as temperatures rose. Empty
50
shells on open rock warmed faster than
occupied shells, perhaps because
living snails retained water or lost
heat through contact with the rock.
On spray-cooled ridges, empty and
55
occupied shells remained closer in
temperature. In crevices, both
occupied and empty shells stayed
cooler than their counterparts on
open rock, yet occupied shells still
60
ran slightly cooler, a smaller gap we
could not assign to a single cause.
These findings suggest two defenses
that may work together: selecting a
cooler location and moderating heat
65
within the shell. But field
observations cannot cleanly separate
every mechanism. A snail in a crevice
may differ from one on a ridge in
size, hydration, or recent feeding. A
70
larger shell stores more heat; a
recently fed animal may rest longer; a
dehydrated snail may be less willing
to crawl. The cove shows us what
animals actually do amid waves, shade,
75
and changing air; it does not by
itself show which physical process
contributes how much.

Passage B

Field studies reveal behavior in context,
but the context can make causes difficult
to isolate. To investigate the Graystone
snails’ internal temperature control, our
5
laboratory tested water loss under
repeatable conditions.
We collected forty-eight snails under a
research permit and allowed them to
acclimate overnight in seawater. The next
10
day, we gently dried their shells and
assigned them to chambers maintained at
24, 30, or 36 degrees Celsius. Half the
snails in each chamber rested on dry
stone; half rested on stone covered by a
15
thin layer of seawater. We weighed each
snail before and after a forty-minute
trial. A separate temperature probe
touched each shell at five-minute
intervals.
20
To make the comparisons fair, we rotated
the positions of the stone platforms
between trials and checked chamber
humidity with a second instrument. We also
assigned snails of different sizes across
25
the treatments rather than placing the
largest in one group. These precautions
reduced simple sources of bias, but they
did not make the chamber a miniature cove.
There were no waves, shifting shadows,
30
predators, or choices among surfaces once
a trial began.
Snails on wet stone lost less mass and
stayed cooler than snails on dry stone at
all three air temperatures. At 36 degrees,
35
however, even the wet-stone group warmed
steadily. After the trials, all snails
recovered in seawater and were returned to
the exact part of the cove where they had
been collected.
40
The results support the idea that contact
with water helps limit heating, both by
supplying moisture and by allowing
evaporation. They do not establish that
evaporation explains the entire difference
45
between occupied and empty shells in the
field. A living snail can alter how much
of its foot touches the rock, withdraw
deeper into its shell, or produce mucus.
Empty shells do none of these things.
50
A second limitation concerns duration.
Forty minutes captured short-term
responses to heat, not the effects of
repeated low tides across a season. We
therefore interpret mass loss as evidence
55
about one trial condition, not as a
prediction of which individual snails will
survive the summer.
Nor should the chamber results be used to
rank every cove location. A spray-cooled
60
ridge may be wet but windy; a crevice may
be dry but shaded. Our controlled trials
simplify that complexity on purpose. In
combination, the studies are most useful:
the field work identifies a pattern worth
65
explaining, and the laboratory work tests
one candidate mechanism while marking the
questions that remain.

Question 1Easier

The author of Passage A discusses possible differences in size, hydration, and feeding primarily to:

Show answer

Answer: D — identify variables that limit a causal conclusion from the field observations.

Those uncontrolled differences could influence temperature or location, so they illustrate why the field pattern cannot isolate each mechanism.

Question 2Mid

The main purpose of Passage A is to:

Show answer

Answer: A — present field evidence that snails manage heat by moving among locations and by moderating heat within their shells, while noting that the cove cannot isolate each cause.

Passage A reports marked snails’ movements and shell temperatures across zones, including the empty-shell comparison, then cautions that size, hydration, and feeding prevent a clean causal split. That combination of pattern and limit is the passage’s purpose. The other choices recast the movement hypothesis as a feeding-route conclusion, overstate what empty shells isolate, or treat size, hydration, and feeding as the variables empty shells were meant to control.

Question 3Easier

In Passage B, the statement that the laboratory precautions did not make the chamber a miniature cove primarily serves to:

Show answer

Answer: A — caution that controlled trials omit shore features that could affect heating.

After listing precautions, Passage B stresses that the chamber still lacked waves, shifting shadows, predators, and surface choices. The remark limits how far the lab can stand in for the cove; it does not explain the wet-stone result or reject the field data.

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