Here is a website that will help you find the answer and understand the poem as well...
http://www.sparknotes.com/poetry/hopkins/section4.rhtml
If you do not wish to visit the site I believe the answer is A.
Because she is mourning her own mortality, because man is mortal.
A. It says in the passage that they declined the preposition
Answer: Yes
Explanation: crocodiles get it and about six species of snakes
