单选题Which of the following statements concerning butterfly valves is correct?（）ASpecial tools are required for lapping or grindingBIt is impossible to throttle flow with a butterfly valveCTo close the valve, it is only necessary to turn the handle a quarter of a turnDThe butterfly valve should never be used in a freshwater system
单选题
Which of the following statements concerning butterfly valves is correct?（）
A
Special tools are required for lapping or grinding
B
It is impossible to throttle flow with a butterfly valve
C
To close the valve, it is only necessary to turn the handle a quarter of a turn
D
The butterfly valve should never be used in a freshwater system
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