Question

a scientist wants to gather evidence related to the following hypothesis: larger packs are more successful a addressing this hypothesis?
the number of pups that survive in large versus small packs.
the age of each animal in large versus small packs.
the number of prey kill by large versus small packs.
the number of packs in a given geographic area.

Explanation:

The hypothesis is about the success of larger packs. The number of prey killed by large versus small packs directly relates to success (as killing prey is a measure of a pack's effectiveness). The number of surviving pups is more about reproduction, the age of animals is about demographics, and the number of packs in an area is about population density - none of these directly measure the "success" as hypothesized.

Answer:

The number of prey killed by large versus small packs.