a friend of my grandfather's will come tomorrow ,I'm wandering how old __ man he might be.A a

问题描述:

a friend of my grandfather's will come tomorrow ,I'm wandering how old __ man he might be.A a
我的老师这题答案是a ,不是the

a(有个单词打错了,wandering应是wondering)
因为还不知道是哪个朋友,所以只能泛指用a