问题补充：
Paper bags produced every year are the world’s production of vehicles.
A. as three times heavy as
B. three times weight of
C. three times the weight of
D. three times as heavier as
答案：
A. as three times heavy as
B. three times weight of
(答案→)C. three times the weight of
D. three times as heavier as
解析：考查倍数和比较等级。倍数必须放在比较等级的前面，常见的结构有：倍数+比较级+than；倍数+as...as；倍数+the weight/size/length of...等。A项的倍数放在了as...as中间，排除A；D项中的as...as中间应该用原级，排除D；B项结构不正确，故选C。
