A beam of light will not bend round corners unlessto do so with the help of a reflecting d

发布时间：2020-08-17 13:19:34

A beam of light will not bend round corners unless    to do so with the help of a reflecting device . 
A. having been made
B. being made
C. made
D. you make

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A. having been made
B. being made
(答案→)C. made
D. you make
解析：unless引起条件状语从句中后面省略了it was。
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