It's most likely D. Here's why:
Answer A- The adverb 'quickly' is describing a verb, not adjective.
Answer B- The adverb 'loudly' is describing a verb, not adjective.
Answer C- The adverb 'sadly' is describing a verb, not adjective.
Answer D- 'Too' is an adverb that is being used to describe 'Cold', which is seen as an adjective in the sentence.
The Library of Congress is one of the biggest database of publications of a wide array of subjects and courses existing in the world. It is a useful site because of the statement found in option B. it has become one of the most credible and trusted sites which scientists depend.
