Answer : Option C) Actually
Explanation : "An adverb is a word or phrase which modifies the meaning of an adjective, verb, or other adverb, expressing manner, place, time, or degree for e.g. gently, here, now, very". There are some adverbs, which are like sentence adverbs,that can be also used to modify the whole sentences.
Here amongst the given options; "Actually" is the word that satisfies the condition of being an adverb as it is modifying the other adverb "really."
Rest all options are a form of adjective.