单项选择题
You must（）in this area unless you have messages about the casualty.
A.keep radio silence B.keep radio silent C.keep radio be silent D.keep silent the radio
单项选择题 You shall（）this letter so as to signify your acknowledgement of the responsibility.
单项选择题 You should not divide the fresh water（）three trips.
单项选择题 Your kind attention to our ship will be（）.
