The correct option is B enthusiastic
It is a verb which expresses eager enjoyment, interest, or approval regarding something.
Option A: It is a noun which means intense and eager enjoyment, interest, or approval.
Option B: It is an adjective; having or showing intense and eager enjoyment, interest, or approval.
Option C: Is a wrong word
Option D: It is an adverb meaning in a way that shows intense and eager enjoyment, interest, or approval.
Option B is the correct answer.