将已沉淀澄清的原水的浊度进一步降低到小于5mg/L，需采用( )来处理。
A．机械加速澄清
B．水力循环澄清
C．离子交换器
D．过滤
参考答案：D
4×8可表示4个8连加。[ ]
— Were you busy last weekend?
— Very. Rather than ____ time playing cards as usual, I devoted every myself to ____ an advertisement. [ ]
A. wasting; making
B. waste; make
C. to waste; make
D. a waste of; making
