11.27 時(shí)態(tài)一致
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　 1) 如果從句所敘述的為真理或不變的事實(shí)，則永遠(yuǎn)用現(xiàn)在時(shí)。
　At that time, people did not know that the earth moves.
　He told me last week that he is eighteen.

　 2) 賓語從句中的助動(dòng)詞ought, need, must, dare 時(shí)態(tài)是不變的。
　He thought that I need not tell you the truth.