Hi shagalo,

This is an example of an inference question. The information in the prompt is essentially just a set of facts - you have to find an answer that is based on (usually a combination) of those facts.

The Facts:
-Bones in the TIP of a bat's wing have LESS mineral content in proportion to organic content
-Bones next to the bat's shoulder have MORE mineral content in proportion to organic content
-The difference in proportions increases biomechanical efficiency (the MORE WEIGHT at the WING TIP, the harder it is to fly).

When dealing with inference questions, I usually look for facts that "overlap", meaning that I can connect the facts. In the prompt, there are a couple of references to the TIP of the bat's wing, so I'm thinking that the correct answer will probably deal with those facts.

The only answer that matches the facts is Answer A. Here's why: the prompt gives us facts to explain biomechanical efficiency (part of why bats can fly). The TIPs of bat's wings have less mineral content....because the more WEIGHT there is in the TIP, the harder the bat has to work to fly. Connecting those facts leads me to think that there's less mineral content and THAT is why there is less weight. Thus, mineral content is heavy. None of the other answers are based on information in the prompt.

GMAT assassins aren't born, they're made,
Rich