The sentence that contains an adverb modifying another adverb is the last option. "Beautiful orchids can grow very successfully indoors."
Very is an adverb that refers to a high degree. Very is modifying the adverb succesfully that makes reference to the way that accomplishes a desired aim or result.
Adverbs have many different meanings and functions. They are especially important in order to indicate the time, manner, place, degree and frequency of something.
