答案：C分析：改为去掉therefore，since与therefor

答案：C分析：改为去掉therefore，since与therefore不连用，同though，but。参考译文：因为鼠类具有破坏性而且可以传输疾病，许多城市都努力灭之。

Kết quả (Anh) 1:

Answer: c analysis: to get rid of therefore,since and therefore is not used with the though,but. Text: because rats are destructive and can transmit diseases, many cities are efforts to fight it.

Kết quả (Anh) 2:

Answer: C analysis: to remove therefore, since and therefore not used in conjunction with though, but. TEXT: Because rodents destructive and can transmit the disease, many cities are trying to destroy it.

Kết quả (Anh) 3:

Answer: C analysis: to remove the therefore, since and therefore do not use, with the though, but. Because the rats are destructive and can transmit the disease, many city try to exterminate them.