问题描述：
关于drop in的用法
drop in 有drop in to do sth吗
eg:Drop in to see us any time.
improper to drop in on him so casually.
drop in on sb
drop by 怎么用
drop in 有drop in to do sth吗
eg:Drop in to see us any time.
improper to drop in on him so casually.
drop in on sb
drop by 怎么用
问题解答：
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