This is a Cannot Be True question so we are looking for the answer choice that directly conflicts with the stimulus (i.e. cannot be true).
This means that the four incorrect answer choices "could be true."
So let's take a look at (E), "The making of hand gestures by hearing babies who have hearing parents should be interpreted as a part of their developing language."
Notice that we have no information in this passage about hand gestures by hearing babies who have hearing parents.
The passage is about hearing babies with hearing parents babbling at a certain age and deaf babies with deaf parents beginning to babble in signs at the same age.
Since we have no information regarding (E), it does not conflict with our stimulus and therefore, could be true. So (E) would be eliminated.
Compare that with (B), "The development of language competency in babies depends primarily on the physical maturation of the vocal tract, a process that requires speech oriented vocal activity."
The example of deaf babies beginning to babble in signs would directly conflict with the idea that the development of language competency in babies depends primarily on the physical maturations of the vocal tract.
As such, (B) would be the correct answer here.
Hope that helps! Please let us know if you have any other questions.
