Question

The river has become much ______ than before because of the waste water from the factories.
A. dirty    B. dirtier  C. Dirtiest

Answer 1

B

解析试题分析：句意：由于来自工厂的废水，这条河变得比以前更脏了。句中暗含现在的河与以前的河相比较，所以应用比较级。故选B。
考点：考查介词短语。