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

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→)A. that, to be improvedB. which, to be improvedC. where, improvingD. when, improving解析：可联系答案网客服索取此答案。

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