D) Marianne ended up revising her report three times: she looked first at the content, then she considered her thesis, and finally she considered questions of style.
This is correct
After many years of trashing China, they are slowly cleaning up.
I am not sure about the first question, I cannot help you with that one, sorry. :/
However, the second question I know. Ragnarok is A), an apocalyptic prophecy, a Norse prophecy stating when the end of the world will come.
The sentence that uses possessive pronouns correctly is
A. That dress looks like yours.
B. Is wrong because it's should be its. It's is a contraction for it is. So it would read - My dog carried it is toy out to the backyard.
C. Is wrong because their should not have an apostrophe s. It should read - The credit for the great food is all theirs.
D. Is wrong because her shouldn't have an apostrophe s. It should read - Those books on the shelf are hers.
Hope this helps :)