---Where do Tom and John sit ?Tom sits of the room and John sits of the room.A. in f

问题补充：

---Where do Tom and John sit ?

--- Tom sits of the room and John sits of the room.

A. in front; at back

B. in the front; at the back

C. in front; at the back

D. in the front; at back

答案：

A. in front; at back

(答案→)B. in the front; at the back

C. in front; at the back

D. in the front; at back

解析：根据题干，本句的意思“汤姆坐在房间的前面，约翰坐在房间的后面”。In front of是指在外面的前部，in the front of是指在里面的前部；at back of是指在外部的后面，at the back of是指在里面的后面。根据题意，所以本题选B。