Which of the following is not a factor which can interfere with the pulse of sound and cause a variation the depth reading?（）

单项选择题Who can contact the Designed Person?（）

A.the designated person
B.the captain
C.all senior officer
D.all officers and crew

单项选择题When shall the stand-on vessel change course and speed?（）

A.the stand-on vessel may change course and speed at any time as it has the right of way
B.after the give-way vessel sounds one blast in a crossing situation
C.when action by the give-way vessel alone cannot prevent collision
D.when the two vessels become less than half a mile apart

单项选择题Carbon dioxide flooding system is used for extinguishing fires because it reduces the concentration of oxygen in the air to（）.

A.flashing point
B.combustion point
C.auto-ignition point
D.lower explosive limit

单项选择题Where shall the key to C02 room be kept?（）

A.In master's cabin
B.In third office's cabin
C.In a break-glass-type enclosure conspicuously located adjacent to the room
D.In a locked locker conspicuously located adjacent to the room

单项选择题Your vessel is crossing a narrow channel.A vessel to port is within the channel and crossing your course.She is showing a black cylinder.What is your responsibility?（）

A.hold your course and speed
B.sound the danger signal
C.begin an exchange of passing signals
D.do not cross the channel if you might impede the other vessel