飞机将旅客或货物运送到其他地方，这种产品或服务的效用称为生产的()。

The statement 'Narcissus met a nasty end'(Line 1, Paragraph 2)implies thatA．selfishness of a boss will be subject to public criticism.B．egotism of chief executives may lead to undesirable consequences.C．a self-centered boss is always troubled with business disasters.D．boss-worship will result in self-asserted leaders. 点击查看答案

丁二烯的用途较大，目前它的主要来源是裂解副产品混合C4通过特殊精馏得到，西欧和日本的全部、美国()的丁二烯是通过这一途径得到的。

A.90%
B.80%
C.70%
D.60%

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