A Class S EPIRB is a（）.

单项选择题A Class C EPIRB（）.

A.is primarily designed for vessels operating up to 50 miles offshore or on foreign waters
B.transmits a signal that can be detected by satellite
C.must be manually activated
D.operates in the medium and low frequency bands

单项选择题A Class A EPIRB is NOT（）.

A.approved by the CCS
B.designed for float free，automatic activation
C.operated on 121.5/243 MHz
D.operated manually

单项选择题A check line is（）.

A.a safety line attached to a man working over the side
B.used to measure water depth
C.used to slow the headway of a barge
D.used to measure the overhead height of a bridge

单项选择题（）is the course to reach you?

A.What
B.How
C.Which
D.When

单项选择题（）is the chain?

A.How
B.What
C.Why
D.How about