单项选择题
A.shape of the anchor
B.stowage of the anchor on board
C.anchor's ability to dig in
D.size of the vessel and its draft
单项选择题 The function of the bypass valve on the self-contained breathing apparatus is to（）.
单项选择题 The extension of the after part of the keel in a single-screw vessel upon which the stern post rests is called the（）.
单项选择题 The exhaust pipe must be gas tight throughout its entire length otherwise（）.