问题描述：
They sent an e-mail to their teacher.
teacher为疑问对象,然后改成疑问句Who did they send an e-mail to?这样改对吗?后面一定要接to吗?
teacher为疑问对象,然后改成疑问句Who did they send an e-mail to?这样改对吗?后面一定要接to吗?
问题解答：
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