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

A.（1）and（2）
B.（2）and（3）
C.（1）and（3）
D.（1），（2）and（3）