其实这四个词可分为两组:

1. “遗忘”之意

① left ＋地点(把东西落在什么地方)；

② forget不加地点。 e.g.

I have forgotten her name.

I left my bag at home this morning.

2. （从高处）落下

① drop跌落

② fall落下 (fell; fallen)e.g.

He dropped the tea cup and it was broken.

The poor man fell off the tree.