A descriptive adjective describes qualities of a noun or pronoun, such as smell, taste, texture, appearance, and shape. The adjectives that are used to describe the nature of a subject or a noun or showing the kind or quality of nouns or pronouns are also called Adjective of Quality. In this sentence, we are describing the readers and the quality of their reading. In the first blank, a descriptive adjective is required which describes the reader. In the second blank, an adverb (a word or phrase that modifies the meaning of an adjective, verb, or other adverbs, expressing manner, place, time, or degree) is required which would describe the verb read.
Option A: slowly is an adverb and hard is an adjective of quality
Option B: slow and hard both are adjectives
Option C: Slow is an adjective and hardly is an adverb
Option D: slowly and hardly both are adjectives.
Option C is correct