Answer:
(a) adverbs,
Explanation:
Words like slowly, very, quickly, fastly and tomorrow that gives the answer to the questions How? are Adverbs. An adverb is a word tells more about a verb, and most of the time answers the questions how often? how? when? what way? where?
Usually, there are five kinds of the adverb, and when the word indicates that how something is done as the question is being asked here, it is called Adverbs of Manner.
