11.27 時態(tài)一致

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

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