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

当待并机与系统频率相差太大，断路器合闸时间又难以把握时，可能会造成（）。

A.系统崩溃

B.同期并列

C.短路

D.非同期并列