Before using or operating any equipment, you should first （） its manual thoroughly and understand its contents（）.

A.the distance between them remains the same
B.the distance between them is changing
C.the position between them is not changing
D.their positions to the earth remain the same

A.the period of time during which no trouble occurs to the engine
B.no trouble will occur to the engine all its life
C.trouble may occur freely to the engine
D.no matter what you do to the engine, no trouble will occur during this period

A.after the point is reached at which the failures begin to increase rapidly
B.before the point is reached at which the failures begin to increase rapidly
C.before the point is reached at which the failures begin to increase slowly
D.after the point is reached at which the failures begin to increase slowly