用于澄清的设备称澄清池,根据其结构型式可分()、()等。
参考答案:机械加速澄清池;水力循环澄清池
---How long __________ your parents ___________?
---For about twenty years.
A.did, marry
B.have, married
C.have, got married
D.have, been married
读下面的图表,回答下列问题。