单选题The boom indicator tells the operator at what angle the boom is compared to the（）.A horizontal position of the boomB vertical position of the boomC horizontal position of the load being liftedD vertical position of the load being lifted

The boom stops are installed on an offshore crane to ______.

A.prevent the boom from being raised too high

B.prevent the boom from swinging

C.support the boom when not in use

D.prevent the boom from being lowered

With a given load on the cargo hook，the thrust on a cargo boom ______.

A.increases as the angle to the horizontal increases

B.increases as the angle to the horizontal decreases

C.is greatest at an angle of 45° and decreases as the boom is raised or lowered

D.is least at an angle of 45° and increases as the boom is raised or lowered

On a crane, the boom indicator tells the operator what angle the boom angle is compared to the ______.

A.vertical position

B.horizontal position

C.boom stop angle

D.minimum radius angle

What does “evel-luffing” accomplish during crane operations ________．

A.It prevents the load from swinging when the boom level is adjusted

B.Less power is needed when topping the boom with a load on the hook

C.It maintains the height of the load above the deck

D.All of the above

The boom indicator on a crane will indicate the ______．

A.Length of the boom

B.Angle of the boom

C.Lifting capacity of the boom

D.Direction of the boom

With a given load on the cargo hook，tension in a single span topping lift ______.

A.increases as the boom's angle to the horizontal increases

B.is at a maximum when the boom is at a 45° angle to the horizontal

C.increases as the boom's angle to the horizontal decreases

D.decreases as the boom's angle to the horizontal decreases

The signal man assisting a crane operator has his arm extended with his fingers closed and thumb pointing upward．This is the signal to ______．

A.raise the boom

B.raise the hook

C.raise the boom and hook

D.check the boom stop

What cargo does a jumbo boom or heavy derrick used for lifting?

The load chart of a ship crane enables the operator to combine the load radius with boom length to determine the ______．

A.Maximum counter weight required

B.Minimum horsepower required

C.Hoist rope strength

D.Allowable load

What is meant by the term“luffing the boom”of a crane ________．

A.Stopping the boom

B.Topping or lowering the boom

C.Moving the boom left or right

D.All of the above