Answer:
The correct answer is very.
Step-by-step explanation:
An adverb is commonly defined as a word that is used to modify a verb, an adjective, or another adverb. Furthermore, it could be said that adverbs provide a description of how, where, when, manner and to what extent something is done.
Bearing in mind the fact that in the sentence provided: "I am very interested in reading the works of Ray Bradbury" interested constitute an adjective and the word "very" is modifying such adjective, it could be said that the adverb this particular sentence is very.