B caused ,因为这里是定语从句的省略,完整的句子应该是：
there is no pullution which/that is caused by traffic;
On Mars,there is no pollution ___ by traffic.A is caused B caused C that caused D that are caused
On Mars,there is no pollution ___ by traffic.A is caused B caused C that caused D that are caused
其他人气：207 ℃时间：2020-01-29 18:45:49
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