Which of the following is NOT mentioned in the passage as the reason for babies' cry

A．Scientists discovered why animal infants cry.
B．The difference in the mount of children's cry is somewhat due to genes.
C．Babies have a violent reaction to the mother's ignorance.
D．Chimpanzees' annoyance can hardly be alleviated.

A．They come to doubt it.
B．They take it seriously.
C．They are indifferent to it.
D．They are weary of it.