It is a wild night indoors, and what must it be in a stone hut upon the moor. What passion of hatred can it be which leads a man to lurk in such a place at such a time! And what deep and earnest purpose can he have which calls for such a trial! There, in that hut upon the moor, seems to lie the very centre of that problem which has vexed me so sorely. I swear that another day shall not have passed before I have done all that man can do to reach the heart of the mystery.

1）为什么是must it be, can it be, can he have 这样的语序 ? 为什么不是it must be, it can be, he can have 这样的语序呢？ 麻烦老师详解一下。

2)  what must it be, What passion of hatred can it be, And what deep and earnest purpose can he have  这3个结构中的what都是what的哪种用法和含义呢？ 3个用法都是一样的吗？

3）And what deep and earnest purpose can he have which calls for such a trial： which的先行词是不是整个“And what deep and earnest purpose” 呢？

4）I have done all that man can do 这里是不是少了一个that, 即I have done all that that man can do = I have done what(=all that) that man can do ?