单项选择题
All echo-sounders can measure the（）.
A.actual depth of water B.actual depth of water below keel C.average depth from waterline to hard bottom D.average depth of water to soft bottom
单项选择题 All electrical appliances aboard a vessel should be grounded to（）.
单项选择题 All entries in logbook,（）made,must not be erased or amended.
单项选择题 All entries in the official logbook must be signed by the master and（）.
