what about going to attending his birthday party tomorrow?

what about going to attending his birthday party tomorrow?
that will depend on my work,but it()be a suitable time for me.
选C mightb为什么不行？表示按经验判断时主要是语气，should 和must表示推断的语气都比较肯定，而might的语气则不那么肯定。所以有时候会有个人理解的差异，如果你认为上下文比较肯定，那么should就是很好的答案。