船台接收到另一船台的中频DSC呼叫，收妥应在（）发出。

A.2187.5kHz

B.2177kHz

C.在接收该DSC呼叫的频率

D.同频段遇险与安全频率

When two power-driven vessels are meeting on reciprocal or nearly reciprocal courses so as to involve risk of collision,they shall be deemed to be in（）.

A.head-on situation

B.crossing situation

C.overtaking situation

D.close-quarters situation