when 可以引導(dǎo)很多從句：
1.賓語從句：例如 I don`t know when he left here.我不知道他上面時(shí)候離開的.此時(shí)when作連接詞引導(dǎo)賓語從句.
2.定語從句：例如 He left his hometown in that year when his father died.他在他父親死的那一年離開了他的家鄉(xiāng).此時(shí)when作連詞修飾that year,引導(dǎo)定語從句.
3.狀語從句：例如 He will go to the doctor`s when it is sunny.當(dāng)天晴時(shí),他就會去看醫(yī)生.此時(shí)when引導(dǎo)狀語,意思是“當(dāng)...時(shí)候”.
4.主語從句：例如When he left here is a question.他上面時(shí)候離開這兒的還沒有人知道.此時(shí)when引導(dǎo)主語從句,意思是“什么時(shí)候”
because 引導(dǎo)結(jié)果狀語從句