I am afraid I am not fit for the job, because it is one         requires a lot of patience.

A．who

B．that

C．what

D．where

泥渣过滤型澄清池可分为：（）

A.水力澄清池和脉冲澄清池

B.悬浮澄清池和脉冲澄清池

C.水力澄清池和机械加速澄清池

D.悬浮澄清池和水力澄清池