115.
W: I often mistake Jim for Bob. Can you tell them apart?
M: No. They look so much alike that even their mother didn't know who was who sometimes when they were young.
答案解析：
正确答案为C。根据I often mistake Jim for Bob. Can you tell them apart?我经常把吉姆错认成鲍勃。你能区分他们吗？可推知，吉姆和鲍勃应为双胞胎，别人经常认错。因此C项正确。

116.
M: What seems to be the problem, Mrs. Allen?
W: I've been having pains in my chest recently.
M: Do you have difficulty breathing?
W: Sometimes. But not too much.
M: Well, let's take an X-Ray of your chest.
答案解析：
正确答案为B。根据having pains in my chest recently最近胸部疼，以及take an X-Ray of your chest为胸部照X光，可推知，二人为医生和患者的关系，因此B项正确。