entering the classroom, remember to take your seat and turn off your cell phone.A. AtB. F

发布时间：2020-08-16 22:09:41

     entering the classroom, remember to take your seat and turn off your cell phone.

A. At
B. From
C. Upon
D. As

网友回答

A. At
B. From
(答案→)C. Upon
D. As
解析：本题考查介词辨析。介词 on/upon后跟 V-ing 形式作“在……时；一……就……”讲，相当于 as soon as 引导的状语从句。
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