Awriter should hyphenate a compound modifier that

C

comes before the noun it modifies.

Explanation:

about 25% of a paper can be direct quotes.

the correct answer is option d. none of these. it is noted that options a, b, and c share the same content.

despite the valid answer provided at the last sentence of each of the options, a question/answer format shouldn't include humourous themed responses such as "you bet your thermal pj's we do." - unless of course, the answer is carried out in an informal environment. this could be replaced with a simple "yes" or "it is necessary".

the question should be re-phrased to a more appropiate syntaxis. instead of "do we need the greenhouse effect? ", it should be written as "is the greenhouse effect necessary? " in order to give it a general scope, instead of limiting the answer to the needs of "we" the humans.