GMAT Critical Reasoning (CR) | Re: A newborn kangaroo, or joey, is born after a short gestation

An assumption is a statement that MUST BE true in order to link the premise with the conclusion. In this question:

Premise 1 (P1): Joey has developed forelimbs to climb into mother's pouch.
Premise 2 (P2): Marsuptial lions have developed forelimbs.
Conclusion (C): Marsuptial lions also needed to climb into mother's pouch.

Option A is not a mandatory link between P1/P2 and C, and hence not an assumption.
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