I must have dropped off to sleep. [V P + to sleep]

我肯定是睡着了。

Just as I was dropping off, a strange thought crossed my mind. [VERB PREP.]

就在我打瞌睡的时候,一个奇怪的念头闪过我的脑海。

Sales to the British forces are expected to drop off. [VERB PREP.]

预计对英国军队的销售量会减少。

The daily toll of casualties has dropped off sharply. [VERB PREP.]

每日伤亡人数已经大大减少。