11.27 时态一致
1)如果从句所叙述的为真理或不变的事实,则永远用现在时。
At that time,people did not know that the earth moves.
He told me last week that he is eighteen.
2)宾语从句中的助动词ought,need,must,dare时态是不变的。
He thought that I need not tell you the truth.