单项选择题
A proper look-out shall be maintained（）.
A.only at night B.only during restricted visibility C.at night and during restricted visibility D.at all times
单项选择题 A proper look-out must be kept（）.
单项选择题 A head-on situation at night is one in which you see（）.
单项选择题 One of the factors which affects the circulation of ocean currents is（）.
