D.when to have
这是“特殊疑问词+动词不定式”的结构,通常可以改为宾语从句,如：
He doesn't know what to do.=He doesn't know what he should to do.
I don't know when to start.=I don't know when I should/will start.
等等,很多.
当主句的宾语和从句的宾语一致时,也就是同一个人时,可以互相改写.
在这里Can you tell me 是表请求礼貌的句型,虽然主语是you,但言外之意是你能告诉我 我们（包括主语在内）什么时候开会吗?
如果选C,应该改为Can you tell me when I/we will have a meeting.
我的解释绝对正确,我是英语老师,如果还有不明白的请说.