The adverbs such as “extremely”, “too” and gently, “quickly” are going to depict the use of word that modifies verb.
The completion of test is required an adverb in the above case, for example, the student completed test quickly. This is forming a correct meaningful sentence without a grammar mistake.
Thus, the options (c), (b) and (a) are incorrect.
The completion of test is required an adverb in the above case, for example, the student completed test quickly. This is forming a correct meaningful sentence without a grammar mistake.
Therefore, the correct option is – d. quickly.