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