Answer:
The correct answer is either hand; modifies basketball.
Step-by-step explanation:
Let's start by clarifying that the adverb is one that modifies a verb, a noun, an adjective or more words.
In this case we find the adverb phrase "either hand". This adverbial phrase is modifying the noun "basketball", and is the one that gives us more information about the way the ball is going to be thrown.