Here's why:
* Alliteration is the repetition of the same consonant sound at the beginning of words that are close together.
In this line, the "w" sound is repeated in "wan," "welkin," and "winds."
Let's look at the other options:
* A) Each us all must his end abide: While there are some repeated consonants ("m" and "s"), they are not close enough to be considered alliteration.
* C) and heavens weep Now is help once more?: There are no repeated consonant sounds at the beginnings of words in this line.