说下理由
问题描述：
说下理由
句型转换：
To look up the words in a dictionaryis helpful for us.(改为同义句)
______is helpful for us ______look up the words in a dictionary.
They are too tired to exercise.(同上）
They don't exercise because they_____ _____ _____ _____.
答
1改为做形式主语的句子．It to
2 他们太累了而不能作操．are tired very much