Question

非限定性定语从句只能用as和which引导吗

Answer 1

as和which引导非限定性定语从句，大多指整个句子，如果指的是具体的人物、地点或时间等，则可以用who/whom/where/when等。
如：
I,who am your friend, will share the work with you.
我是你的朋友，将与你分担这项工作。
Lastyear I visted the People's Great Hall, where many important meetings are heldevery year.
去年我参观了人民大会堂，每年许多重要会议都要在那里举行。
I　congratulate my neighbour, whose son has just won the election.
我祝贺我的邻居，他的儿子刚刚赢得选举。

Answer 2

其实非限制性定语从句和限制性定语从句的引导词基本一样
除了非限制性定语从句不能用that和why引导外，其他的像是which,
who,
when,
where
这些都可以。

Answer 3

非限定性定语从句
1 引导非限定性定语从句的关系代词有： who , whom .whose = of whom / of which , which , as
2引导非限定性定语从句的关系副词有： when , where
3 使用非限定性定语从句的情况有：
（1）当关系代词指代整个主句内容时，用which引导
She said she hadfinished her work , which I doubted very much .
（2）当先行词是世界上独一无二的事物或专有名词时
The moon , which is384,400 kilometers away from the earth , creates many beautiful stories .
（3）先行词指的是只有一个亲属（ son , daughter , father , mother ,sister ,brother ,wife , husband …）
l My father , whois an excellent engineer , is leaving for Canada .
l My sister , whoworks in Shanghai,sends me an E-mail almost every day .（我只有一个姐姐）
l My sister whoworks in Shanghai,sends me an E-mail almost every day .（除了在上海的姐姐外，还有其他姐姐）
（4）当出现 some , many , few , a few , little , much , most , two ofwhich / whom …
I have three foreignteachers , two of whom are from Canada.