1.用and和but,或者,which连接的两个句子时,主语和时态可以前后一致,也可以不一致。
2.你的例句she finally understands her sisister's words which she had not understand in the past. 时态明显错误,必须把从句中的understand改成understood.
3.understand英[ˌʌndəˈstænd]美[ˌʌndərˈstænd]
v.懂; 理解; 领会; 了解; 认识到; 明了; 谅解; 体谅; 得知; 默认;
[例句]People are often afraid of things they don't understand.
人往往对自己不懂的东西感到恐惧。
[其他] 第三人称单数:understands
现在分词:understanding
过去式:understood
过去分词:understood
4.时态一致是指句子的时态必须从头到尾都是一样的。即
谓语动词的时态与时间状语的时态一致,从句的谓语
动词时态与主句保持一致,直接引语的时态和
间接引语的时态转换一致。但已经存在例外,例句如下。
(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.
5.句子中如果有两个以上谓语动词,那么就可能同时出现2种以上时态,因为时态只是用来表述事件和状态的,该用什么就用什么。
(1)并列谓语一种时态的例句。
Yesterday I went shopping, bought some books and had dinner at a good restaurant.
The soldier looked at him, exchanged glances with his comrade and took out the gun.
(2)并列谓语多种时态的例句。
A fire sale of at least $20bnworth of equities roiled stockmarkets on an otherwise unremarkable Friday and has left at least two global banks—Credit Suisse and Nomura—facing multibilliondollar losses.
前面用
过去时表示那个事件是过去发生的,后面用
现在完成时表示至今的影响。