The word Wunderkind probably means______.

A．all HIV carriers are doomed to die
B．only those who show clinical evidence of AIDS can pass on the virus to others
C．the number of AIDS cases will be reduced in the 1990s
D．IV drug users are a high-risk group of people vulnerable to AIDS infection

A．They enable the bat to determine the size of the target.
B．They help identify the range of widely spaced targets.
C．In some species, they enable the bat to judge whether it is closing in on its target.
D．In some species, they help the bat to tell the shape of the target.