Argument Mapping:

Mole eats underground crops BUT farmers are concerned it will eat above-ground crops
Farmers need not worry --> mole has predator birds, would eat them if the came above the ground.

Conclusion: Mole poses no threat to above-ground crops

Pre-think the assumption: What if the mole comes out to feed only during nighttime when the birds are not active?

D is a close paraphrase of the above. This can also be verified by the Negation Test.
Negation: The feeding time of the Mole is not the same as that of the predator birds --> The mole would come out of the burrow at a different time and eat away all the above-ground crops!

This test DESTROYS the conclusion completely.
[spoiler]Answer : D[/spoiler]

Regards,
Vivek

Mike@Magoosh wrote:The Spotted Mole is a rodent that burrows underground and eats all forms of vegetable matter. Farmers are concerned that this mole could eat some of their commercial fruits, planted in above-ground planters and bins. The farmers need not worry about the Mole, though, because throughout the region in which the Spotted Mole is found, birds of prey such as hawks and falcons are active, and these birds would prey upon the Spotted Mole if the mole came above ground at all. Therefore, the Spotted Mole poses no threat to these totally above-ground fruits.

Which one of the following is an assumption on which the argument depends?

(A) The birds of prey capture and kill every single Spotted Mole that comes above ground.
(B) Some land-based mammals active in this region, such as fox, will also hunt and eat the Spotted Mole on a regular basis.
(C) No other animal could pose as significant a threat to the above-ground fruits as could the Spotted Mole.
(D) The times of day the Spotted Mole feeds are the same as the times of day that the birds are prey are in the air.
(E) Larger burrowing mammals, such as badgers or weasels, can dig up the burrows of the Spotted Mole, endangering those that remain underground.

For a discussion of Assumptions and the Negation Test on GMAT CR, as well as for the OA & explanation of this particular question, see:
https://magoosh.com/gmat/2013/assumption ... -the-gmat/

Mike

D is the correct answer here. If the mole and the prey have the different times suppose if mole comes out of the ground in the night when the birds are not looking for prey then argument falls apart. So D is the assumption.