刘老师和黎老师的解答都很好，我完成同意。这里再提供《现代英语惯用法词典》（费致德编著）关于 each other 和 one another 的几点用法说明，以供 speed_eriko 网友作补充参考：

1. each other 原指两人之间互相，彼此；one another 原指两人以上之间互相，彼此。在现代英语中已不加区别，可以通用。例：

We help each other all the time.

Some / A few / Most / Three or four / of us know each other pretty well.

The just struggles of the people of all countries support each other.

The two men shook hands with one another.

2. each other 的 each 原系主语；other 原系宾语。例：

The two sisters helped each other = each helped the other. 现代古风的书面语言仍有把 helped each other 写为 each helped the other的。

3. each other 的所有格应是 each other's；不可写成 each others'。

4. each other, one another 不能作主语用。

（误）We know what each other wants.

（正）We each know what the other wants.

（误）We know what each other thinks.

（正）We each know what the other thinks.

或each of us know what the other thinks.

如系三个人或三个以上的人，可说：

We each know what the others think.

Each of us knows what the others think.

（误）We know how one another is getting along.

（正）We each know how the other is getting along.

或 Each of us knows how the other is getting along.