1975年7月15日，“联盟19号”飞船和“阿波罗号”飞船在太空对接成功，苏美两个航天大国的（）名宇航员完成了首次国际合作考察飞行。
参考答案：5
A distress signal（）.
A.consists of 5 or more short blasts of the fog signal apparatus
B.consists of the raising and lowering of a large white flag
C.may be used individually or in conjunction with other distress signals
D.is used to indicate doubt about another vessel's intentions
