those boys helped one another in their studies

问题描述:

those boys helped one another in their studies
A each other B one another C one and another D each and other
请问为什么呢
这四个都是互相的意思 可是有什么不同呢

each other 指两者之间;而本题的主语是those boys,指三者或三者以上用的是one another.