What makes the theremin a unique musical instrument? You play it without touching it. When you

Choice B is the best answer. The convention being tested is the use of plural nouns in a sentence. The plural noun "hands" and the plural noun "antennas" correctly indie that two hands are placed between two antennas when playing the theremin.

Choice A is incorrect because the context requires the plural nouns "hands" and "antennas," not the singular possessive nouns "hand’s" and "antenna’s." Choice C is incorrect because the context requires the plural nouns "hands" and "antennas," not the plural possessive nouns "hands’" and "antennas’." Choice D is incorrect because the context requires the plural noun "hands," not the plural possessive noun "hands’."