drop off
1．fall off掉下
My top button has dropped off and I can't find it．我最上面的钮扣掉了，找不到了。
2．become fewer or less；decline 减少；下降
The number of students has been dropping off recently．近来学生人数减少。
Sales have been dropping off badly．销售额下降得厉害。
Attendance at football matches has dropped off since the coming of television．自有电视以来，到现场观看足球比赛的人就减少了。
3．fall asleep睡着
I was just dropping off when the telephone rang．我刚要睡着，突然电话铃响了。
4．let sb．get down from a vehicle；set down让某人下车；放下
Where do you want me to drop you off？你要我在哪儿让你下车？
Tom dropped me off at the postoffice and I've walked the rest of the way．汤姆让我在邮局下了车，剩下的路我就步行了。
He said he would drop the parcel off at the post office．他说他要在邮局寄一个包裹。
I can drop the laundry off on my way to work．我可以在上班的路上把要洗的东西送掉。