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）