OA is E

OE given in the site

This question focuses on verb tense and agreement, as well as general rhetorical construction. In this sentence all of the verbs agree with their subjects. However, the phrase before reaching the stomach does not have a clear subject. It appears to modify they, the chickens, instead of food. The present tense verb swallow should be replaced with the present perfect verb have swallowed in order to indicate that the swallowing occurred before the use of the stones.

1. The phrase before reaching the stomach does not have a clear subject. It appears to modify they, the chickens, instead of food.The present tense verb swallow should be replaced with the present perfect verb have swallowed in order to indicate that the swallowing occurred before the use of the stones.
2. The singular verb is does not agree with the plural subject stones. Is should be in the plural form are.
3. swallow should be in past perfect have swallowed
4. The phrase before reaching the stomach does not have a clear subject. It appears to modify they, the chickens, instead of food. The singular verb is does not agree with the plural noun stones. Is should be in the plural form are.
5. This sentence is correct as is. In this sentence all of the verbs agree with their subjects and are in the correct tenses. The modifying phrases do not allow for any confusion.

Tommy Wallach wrote:Hey All,

People seem to have the right general idea in this one, but there are a lot of general errors. First of all, the verb "have swallowed" is in the PRESENT PERFECT tense. The official website this comes from (Platinum GMAT) also has it written as "past perfect". This is incorrect. Some people seem to be suggesting that we need the past perfect because we need to describe a completed action. That's a dangerous way to put it, because the present perfect is used to describe an action that began in the past, but continues into the present.

To be honest, I don't think this is a legitimate GMAT question (Sorry Platinum), because it hangs on a very small grammatical issue that you could argue against. That said, E is the better answer choice, because it clarifies that chickens don't go out to eat rocks AFTER they've eaten. However, the present tense can be used for eternal states. For example, in the sentence "The food I eat sometimes makes me sick", it's clear that the eating of food is occurring before the sickness, even though we didn't use the present perfect.

So, while E is correct, I think this issue is too small for a real question to hang on it. I'm open to disagreement, however! : )

Hope that helps,

Tommy Wallach
ManhattanGMAT

Agree completely. Certainly not a GMAT level q.