drop in on/drop in at

有区别。虽然 drop in on 与 drop in at 都作“顺便访问”解，但它们后接的宾语是不同的。drop in on 接表人的名词或代词：

1. They dropped in on us as they were passing through town. 当他们路过镇子时,他们就来看我们。

2. Please drop in on me next time you come over. 下次过来时,请来看我。而 drop in at 接表处所的名词(参见 call at):

3. I dropped in at the club on my way home. 在回家的路上我顺便去了俱乐部。

4. Let's drop in at Tom's. 让我们去汤姆家坐坐。