摘要:17.D本句考查动词的被动语态和时态.it+is+动词ed形式.to do是固定的搭配用法.而Bunsen Burner的发明是过去发生的动作.所以用完成时态.
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用-ing形式的被动语态合并句子
You can’t imagine what great trouble they have solving the problem.The problem is being talked about.
=You can’t imagine what great trouble they have solving the problem ________.
用-ing形式的被动语态合并句子
I had taught the boy many times.The boy still didn’t know how to do the exercised.
=________, the boy still didn’t know how to do the exercises.