【单选题】
Which of the following operating features do displacement pumps bear if they are working under no-cavitation condition?（）<br /> (1) output is almost directly proportional to speed<br /> (2) they are self-priming<br /> (3) they will develop a discharged pressure equal to the resistance to be overcome, irrespective of speed
A、（1）and（2）
B、（2）and（3）
C、（1）and（3）
D、（1），（2）and（3）
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