单项选择题
Proper use shall be made（）radar equipment if fitted and operational.
A.of B.to C.on D.with
单项选择题 Keep clear（）the buoy.
单项选择题 In the International Code of signals，a group of three letters indicates（）.
单项选择题 In order to prevent galvanic corrosion，an aluminum boat must be insulated from the davits and gripes. Which of the following is acceptable as an insulator?（）
