下列选项中，会引起泵内有杂音的是（）。
A、轴承无油
B、部件损坏
C、泵抽空
D、出口阀开度小
参考答案：A, B, C, D
Read and choose. 慧眼识珠，单项选择。
John: ___
A. Nice to meet you, too!
B. See you again.
2. Lily:___
Sam: You're welcome.[ ]
A. How about you?
B. Thank you very much.
3. Cathy:
Jake: At half past seven.[ ]
A. What do you do?
B. When do you get up?
无细胞壁结构的微生物是
A．革兰阴性细菌B．真菌C．支原体D．立克次体E．衣原体的原体
