It's definitely D.
It's for sure not C. And I've never read the full story, but this passage doesn't indicate a depressing mood of foreshadowing danger. And the vocabulary in the writing doesn't impact the story itself.
Two main factors: The Norman invasion and political unification. The Norman invasion introduced a great many French loanwords, some 40% of English vocabulary by Chaucer's time.
A because global warming is really occuring
