Question

要怎么看哪一个是主句哪一个是从句呢

比如：Not until i shouted at the top oa my voice did he turn his head .那个是逐句那个是从句呢？

Answer 1

这一句话是一句否定词开头的倒装句，一般用来表示强调。
主句就是全句的 至少是主语和谓语所在的地方，所以如果你对句子的结构熟悉的话你可以找主语谓语来确定主句。
但是更简单的方法是找引导词 which when where whose that if whether等等，跟在引导词后面的就是从句。
比如，你给出的例句它可以改写成: He turned his head when I shouted at the top of my vioce.或者When I shouted at the top of my voice, he turned his head.意思不变。这是一个when引导的时间状语从句，意思是when后面的从句在主句中充当状语的成分。在这句中 主语是 He 谓语是turned，主句就是He turned his head ，从句由when 引导，从句就是I shouted at the top of my vioce。
然后回到Not until i shouted at the top of my voice did he turn his head.这句话，主句是 he turn his head，从句就是 i shouted at the top of my voice 。只不过这里是个倒装句型，要注意语法。
如果你难以判断这种类型的主句和从句，那就建议你先将它改写成when之类的引导词引导的正常语序的句子，然后再用'when'后面的就是从句，这样的法则就可以了。

原创手打，给最佳吧~
希望能帮到你。

Answer 2

这个是由于 not until 放于句首引起的倒装，恢复成陈述句就是
He didn't turn his head until I shouted at the top of my voice.
这句话中，He didn't turn his head是主句， until I shouted at the top of my voice.
其实判断主句从句很简单，有引导词的那句话就是从句。比如说，
I got up when my mom came in.
引导词是when, 所以 when my mom came in.