（50分）关于定语定语从句的一些小问题
3个回答
1 可以,例如：This is a house,in which we once lived.非限制性定于从句的一个特点时去掉定于从句后不影响原句意思,也可以说只要不影响原意,都可以用非限制性定于从句（多说一点,如将上面那句话说成This is the house in which we once lived,此时用the就是定于从句,不能用非限制性定于从据,即定于从据不能省略）
2 可以,成为表语从句,用where引导,表示地方.其他表语从句例子：
The problem is when we can get a pay rise.
He has become what he wanted to be ten years ago.
(另外你的原句是不是该说成This house is the one we were once invited to.)
3 是的,as只能引导整个句子,且一般放在句首,如：
As we know,smoking is harmful to one's health.
当然也可以是强调内容的不同而将位置改变,如强掉吸烟有害而不是人人皆知,可说成Smoking is harmful to one's health,as we know.
