单项选择题
A.slack enough to allow slight leakage of fluid
B.slightly clocked
C.brought up tight so as not to allow any leakage
D.fitted with a relief valve
单项选择题 Which of the following pumps is used where a relatively high pressure and small capacity are required?（）
单项选择题 The （） pump discharges a nearly constant amount of liquid regardless of pressure.
单项选择题 Which of the following operating features do displacement pumps bear if they are working under no-cavitation condition?（） (1) output is almost directly proportional to speed (2) they are self-priming (3) they will develop a discharged pressure equal to the resistance to be overcome, irrespective of speed