问题
选择题
The river has become much ______ than before because of the waste water from the factories.
A. dirty B. dirtier C. Dirtiest
答案
答案：B
题目分析：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。
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