Psycholinguists know that a child produces speech by imitating adults,

Psycholinguists know that a child produces speech by imitating adults, but they do not know how he learns to distinguish significantly different phonemes or how he comes to ignore meaningless variations among speech sounds.

A) by imitating adults, but they do not know how he learns to distinguish significantly different phonemes or
B) by imitating adults, but they do not know either how he learns to distinguish significantly different phonemes nor
C) through the imitation of adults, but they neither know he learns to distinguish significantly different phonemes nor
D) through the imitation of adults, but they do not know either how he learns to distinguish significantly different phonemes nor
E) by imitating adults, but they do not know how he learns to distinguish significantly different phonemes nor