A.under towB.fixed to the seabedC.underwayD.All of the ……

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

单项选择题A major health hazard of the product tert-butylamine is that it （）.

A.can be absorbed through the skin
B.causes irreversible damage to eye tissue
C.is a very unstable product
D.All of the above

单项选择题A low pressure annular preventer which is used to direct flow of kick fluids away from the rig floor is called a （）.

A.dump valve
B.deflector
C.separator
D.diverter