"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
正确答案是B
"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
正确答案是B