状语从句中的两个句子之间必定有一连词,如and but as 各举一例.

首先,and,but连接的并不是状语从句.as是可以作为状语从句的连接词的.
and和but叫做并列连词,连接状语从句的叫做从属连词.
My sister cried and I felt sad too.
I don't like Enlish but I have to take it.
Young as he is,he knows a lot.