as的非限制性定语从句，可以放在句首，可以放在句中，也可以放在句末。例子：
1.Taiwan belongs to China,as we all know.
众所周知，台湾属于中国。
2.People can't live without air or water, as we all know.
没有空气和水，人就不能生存。
3.As is known to all, China is a developing country.
众所周知，中国是一个发展中国家。
4.Jack was late for school, as often happened.
杰克上学又迟到了，这是常有的事。
1.As we all know， China is a great country which has a long history.
2.As is mentioned above，learning English well is of great inportance to us students.
3.As is often the case with Tom，he was late again this morning.
4.As was reported earlier，that area was destroyed by a strong earthquake.
