问题： [单选,材料题] Air transport companies use different planes__________.
A . in the development of air transportation
B . the earliest passenger flights were successfully operated
C . to make travel easy and pleasant for the passengers
D . to provide different services
E . the shortage of qualified pilots
F . traveling by air was very cheap
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发表于 2022-3-16 20:03:34
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发表于 2022-3-17 13:41:02
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