There is a new problem involved in the popularity of private cars road conditions need .

问题补充：

There is a new problem involved in the popularity of private cars road conditions need .

A. that, to be improved

B. which, to be improved

C. where, improving

D. when, improving

答案：

(答案→)A. that, to be improved

B. which, to be improved

C. where, improving

D. when, improving

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