A.at anchorB.being towedC.agroundD.drillingA mobile off……

单项选择题A mobile offshore drilling unit under tow is approaching a fog bank. When should fog signals be started? （）

A.When the towing vessel enters the fog
B.When the drilling rig enters the fog
C.When the towing vessel can no longer be seen from the rig
D.Immediately

单项选择题A mobile offshore drilling unit must display obstruction lights when it is on the waters over the Outer Continental Shelf and is（）.

A.under tow
B.fixed to the seabed
C.underway
D.All of the above

单项选择题A message by flashing light consists of the call，the identity，the text，and the （）.

A.destination
B.answer
C.time
D.ending

单项选择题A mean sun is used as the reference for solar time for three reasons. Which reason is NOT a cause for use of a mean sun?（）

A.The motion of the apparent sun is along the ecliptic
B.Measurement of time is along the celestial equator
C.The speed of the Earth's revolution is not constant
D.There are variations in the Earth's rotational speed

单项选择题A marine chemist issues gas free certificates and is certified by which organization? （）

A.Mine Safety Appliance Association
B.American Chemical Society
C.Marine Chemists Association
D.National Fire Protection Association