从神庙的链接复制的，不知道对不对
There is a simple rule, which has only three exceptions:
OW is used:
1. at the end of a word eg how, cow
2. at the end of a syllable within a word eg flow-er, tow-el
3. before 'n' or 'l' if they are at the end of a word eg brown, howl
OU is used in every other case....
... with the following exceptions: noun
foul
crowd
