簡單地說，一句話中不只一個謂語的時候就肯定有從句。

1）主語從句：一個句子在復合句中充當一個主語，如：What we need is time.如果從句較長，謂語又較短，避免頭重腳輕，可用it作形式主語，而將從句放在句末。如：It is said\eported\\estimated\\has been proved that......2）定語從句：定語從句修飾的先行詞可以是名詞或代詞，也可是句子。定語從句通常位于先行詞之后，由關(guān)系代詞或關(guān)系副詞引導。如：The girl whose parents died in an accident is living with her grandmother. 3）引導目的狀語從句的連詞有：so that,in order that,for fear that等，從句常使用may,might,can,could,would等情態(tài)動詞。如： We got up early this morning so that we could catch the first bus to the railway station.