教材例句：As Tan once said, Chinese music should… 谭盾曾说过，中国音乐要……。该句为as引导非限制性定语从句。
知识点分享：As引导非限制性定语从句
as 引导非限制性定语从句时，具有以下特点：
一、位置灵活
as 引导的非限制性定语从句可以位于句首、句中或句末。例如：
As is known to all, the earth moves around the sun.（位于句首）
The earth, as is known to all, moves around the sun.（位于句中）
The earth moves around the sun, as is known to all.（位于句末）
二、指代内容
关系代词 as 在从句中作主语、宾语或表语，指代整个主句或主句的一部分内容。例如：
As we all know, he is a good student.（as 作 know 的宾语，指代后面 “he is a good student” 整个句子）
He is a good student, as is known to us all.（as 作主语，指代 “he is a good student”）
三、常见结构
1. as we all know /as is known to all：众所周知。
例如：As is known to all, China is a country with a long history.众所周知，中国是一个历史悠久的国家。
2. as is often the case：情况常常如此。
例如：As is often the case, he comes to school late.情况常常如此，他上学又迟到了。
3. as has been said before：如前所述。
例如：As has been said before, we should pay attention to our pronunciation.如前所述，我们应该注意发音。
4. as often happens 正如经常发生的那样。
例如：As often happens, the bus is late again.正如经常发生的那样，公交车又晚点了。）
5. as we expect 正如我们预料的一样。
例如：The experiment succeeded As we expect.正如我们预料的一样，实验成功了。）
某人所说。
例如：As the teacher puts it, “Practice makes perfect.”正如老师所说：“熟能生巧。”
四、与 which 引导的非限制性定语从句的区别
1. 位置不同：which 引导的非限制性定语从句不能位于句首，而 as 引导的非限制性定语从句可以位于句首。例如：As is mentioned above, the number of the students in our school is increasing.（不能用 which 替换 as）
2. 含义不同：as 引导的非限制性定语从句有 “正如，正像” 的意思，而 which 引导的非限制性定语从句没有这个意思。例如：He is late again, as is often the case.（强调 “正如经常发生的那样”）；He is late again, which makes his teacher very angry.（which 指代他又迟到这件事，不含有 “正如” 的意思）