单项选择题
A rope ladder with wooden rungs is a（）.
A.drop ladder B.life ladder C.Jacob's ladder D.jury ladder
单项选择题 A pelican hook（）.
单项选择题 A common class of wire rope is the 6X37 class.What does the 37 represent（）.
单项选择题 A Chinese stopper（two lines）will hold best when you（）.
