题目内容
写出下列单词或词组的正确形式
In the 1700s, many scientists were ________ ________
（从事于）the steam engine.
答案：working;on
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写出下列单词或词组的正确形式
In the 1700s, many scientists were ________ ________
（从事于）the steam engine.阅读快车系列答案