at the doctor's 可以换成 in the doctor's吗？

我在看医生。
I am at the doctor's.
可以换成
I am in the doctor's. 吗？
为什么不能呢？最好能说说原因。
在理发店里都能说in the barber's,
在看医生为什么就不能说in the doctor's 呢？

They are waiting -----.A at the doctor B at the doctor's C. in the doctor d.in doctor at the doctor's at Mr Greens' He arrived at the doctor's at twenty ___five. The doctor insisted that he _____somking at once. Where were you this morning?I was ___.I had a bad cold.A.at the doctor B.at the doctor's选哪个? 关于while he yan was at the doctor's. l was going to the class英语短文 翻译THE NEW DOCTOR what did the doctor say? “Doctor No”和“Mack The Knife ”是什么意思？ the doctor ___is going abord quit son