选B吧,the teacher (the boy is talking to ) is leaving for Japan next Sunday.和那个男孩讲话的老师下个星期天将去日本.
这里是the boy is talking to 是定语从句,修饰teacher,teacher作为先行词在定语从句中做to 的介词宾语,先行词在定语从句中作宾语,关系代词可以省略,所以这句话完整应该是the teacher(whom) the boy is talking to is leaving for Japan next Sunday.
再者,我们需要熟悉talk 的短语,talk to/with sb与某人交谈,talk about sb谈论某人.所以这里CD答案talking 后面都应该加上about