When a caterpillar emerges from the egg on a tree branch, it immediate

We know that the caterpillar usually climbs upward. This behavior could be explained by "an innate tendency to move in the direction opposite to the pull of gravity." This explanation has nothing to do with light.

If we put a strong light at the bottom, the caterpillar will climb downwards. If the gravity explanation were valid, the caterpillar would climb upwards regardless of what's going on with the light. Now we have evidence that the caterpillar's movement has nothing to do with gravity. Instead, the caterpillar simply moves towards the strongest light source. Normally, this would be the sun, explaining the usual upward movement.

You might think, "Well, how do we know that the caterpillars are moving upwards when the sun is out?" True, we don't know for sure. But the information in the passage best supports choice (C).
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When a caterpillar emerges from the egg on a tree branch, it immediately climbs upward until it finds a leaf bud to eat.
Old hypothesis: They have a tendency to move in the direction opposite to the pull of gravity.
(Pull of gravity is downward and they move upward so the hypothesis was that they move against gravity)

In a recent experiment, a strong light source was placed at the bottom of a tree, and caterpillars, after hatching, climbed downward.
(This experiment showed that the gravity hypothesis was not correct. The caterpillars moved downward in case of a strong light source at the bottom)
So it seems that the caterpillars are driven by light. That they move in the direction of the brightest light available.
Normally, a tree would be lit by sunlight and since it is stronger at the top than at the bottom, the caterpillar moves upwards. A strong light at the bottom of the tree would make the bottom more lit than the top. That would explain why the caterpillar moved downwards in that case.
Hence, (C) makes sense.

Certain words clarify the intention. The use of "strong light" in the argument implies that the bottom of the tree would be more brightly lit.

D. Newly hatched caterpillars move toward the leaf bud nearest to them.

This is not supported by the argument. They move in the direction that suits them till they reach a leaf bud. Normally they move upward. When there is a strong light at the bottom, they move downward.

Answer (C)
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No, we don't need to assume that anything is brighter than the sun in order to choose (C).

Choice (C) states that newly hatched caterpillars move towards the strongest light source in the environment.

This is not the same as saying that newly hatched caterpillars move towards the strongest light source on the planet. It might be the case that in the immediate environment of the newly hatched caterpillars, available sunlight (not literally the sun, but the light that comes from the sun) is not as strong as whatever light source biologists placed at the base of the tree. Given that we're talking about a tree here, it would make perfect sense that the tree's own leaves block some sunlight from reaching the caterpillar's environment.

As I mentioned earlier, we don't know the precise sunlight conditions, but the information that we do have supports (C) more than it supports any other choice.

I hope this helps... um, shed some light on the situation?
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Here's a video explanation.

argument clearly points to light source either sun or light source. so conclusion that show this will be right one and C does that exactly.

Answer: C

GMATNinja VeritasPrepKarishma

When a caterpillar emerges from the egg on a tree branch, it immediately climbs upward until it finds a leaf bud to eat at night time.

Do we not NEED highlighted text to mentioned in the argument?
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With the placement of artificial light we have to assume that it is brighter than the sun? How can we assume something is brighter than the sun?

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Hi GMATNinja mcelroytutoring VeritasKarishma

D. Newly hatched caterpillars move toward the leaf bud nearest to them.

Why can't D be an answer?

My reasoning:
When a caterpillar emerges from the egg on a tree branch, it immediately climbs upward until it finds a leaf bud to eat. Biologists thought that this behavior displayed an innate tendency to move in the direction opposite to the pull of gravity.
It doesn't mean it moves in direction or opposite to gravity but it moves to the nearest leaf bud.

2nd , i can't relate with ligh source here. Should not the argument mention that leaf bud was kept downward then it moved downward.

I shortlisted C vs D. Then i found lost how to choose C or D

Please suggest GMATNinja mcelroytutoring @ VeritasKarishma

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