动词只有在倒数第二个字母是元音字母时才需要这么变，元音字母包括A,E,I,O,U，而study倒数第二个字母是D非元音。

studying：v.学习;攻读;审视;端详;细看;研究;调查

例句：

He's studying music in his spare time.

他在空闲时间学音乐。

I am studying Chinese.

我正在学中文。

The students were questioned on the books they had been studying.

学生被问到有关他们所学课本内容的问题。

She's studying art history.

她正在研读艺术史。