Messages be changed from sound into electricity before they be sent by radio. A.
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Messages______ be changed from sound into electricity before they ______ be sent byradio.
A. must;will B. have to; can C. can;must D. need; may
试题答案
【答案】
B
本句意思是“信息得从声音转化成电子信号才能被送出去”。must和have to都可以翻译成“必须”，往往可以互用，但must表示的是说话人的主观看法，而have to则强调客观需要，如：The film is notinteresting. I really must go now.
I had to workwhen I was your age.
本题很明显是强调客观需要。