inflection center

例句：

1. 1. The inflection center is the point where a word changes its meaning.
   发音中心是单词意义改变的地方。
2. 2. The inflection center of English is the vowel sound.
   英语的发音中心是元音音素。
3. 3. The inflection center of a sentence is the punctuation mark.
   句子的发音中心是标点符号。