问题描述：
这个单词怎么不是过去式?
He lent me a book,I read a few lines ,but I did not understand a word.这句话中的understand 怎么不是understood?
He lent me a book,I read a few lines ,but I did not understand a word.这句话中的understand 怎么不是understood?
问题解答：
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