听力原文：W: Hey, you have so many clocks in your bedroom. But is there something wrong wit

h your clocks？ None of them has the same time.

M: I do it on purpose. I set this yellow clock ahead ten minutes, and this black one back ten minutes, but I always set that green one to the right time.

Q: What can we learn from the conversation？

(19)

A．The man has only two clocks in his bedroom.

B．The yellow clock keeps the right time.

C．The black clock is ten minutes slow.

D．The green clock is ten minutes ahead of time.