问题
选择题
If you are free to walk through out city, please ________ us.
A drop in B drop in at C. drop in on
答案
答案：C
题目分析：A.drop in 顺路拜访，B drop in at +地点顺路拜访某地，C.drop in on sb.顺路拜访某人。句中是us，故选C。
点评：完成本题需要了解固定搭配at加地点，on加人。