单项选择题
At least（）radar transponder shall be carried on each side of every cargo ship of 500 gross tonnage and upwards.
A.one B.two C.three D.four
单项选择题 As you hold a piece of manila line vertically in front of you，the strands run from the lower left to the upper right.Which type of line is this（）.
单项选择题 An intermediate spring is（）.
单项选择题 A spanner is a（）.
