does it matter_____ will represent us to attend the meeting?A you think whoeverB who do you thinkC you thinkD who you think能不能告诉我为什么不能选B?

前面是does it matter+句子
it形式主语
指代you think who will represent us to attend the meeting 这件事
如果再加 do 那是两个句子了，放在一起，显然句子成分就不正确了

I read about it in some book or other. does it matter what it was?(A)
注：用which不好，因为一般应该说"does it matter which one it was"，只用which不通顺。而用what意思相像，但是绝对通顺
getting water is not the least 的意思是其中一个问题就是取水.in another word, getting water is not the only problem.
please tell me how you would like to have your coff, black or white(上面答题的那位终于答对一题)
以我在澳大利亚的7年经验保证答案的准确率。

这句话可改为肯定的强调句句：（Who you think will represent us to attend the meeting） does matter.括号中的部分充当主语。

does it matter 已经成分全了
后面相当一个it 的从句 即主语从句
从句中一律用陈述语气

因为这是主语从句,形式主语是it.在从句中,用称述句式,所以选D

?does it matter_____ will

B who do you think

D who you think
答案是D，能不能告诉我为什么不能选B？
这种体用还原法，肯定句式：you think （who will represent us to attend the meeting ）does matter 你认为。。。重要。