He got the first prize,----- made us very happy.

这是一个非限定定语从句,as和which都可以引导它,作主语成分
但是当as在从句中做主语时,后面常接动词的被动语态
如果从句中的行为动词是主动语态,一般用which
比如
She has been absent again,as is expected.
Tom has made rapid progress,which makes us very happy.