Answer:
The answer is D) Alternating ensembles of contrasting size
Explanation:
The etymology of the word concerto can be traced back to two different Latin words, one is Conserere (to tie, join, or agreement) and the other is Concerto, concertare, concertatus (to contend, competition or fight). This derivation probably comes from the idea that the two parts in a concerto (the soloist and the orchestra or concert band) alternate between opposition, cooperation and independence to create a sense of flow. So it's a constant alternation of ensembles (the soloist-s and orchestra) back and forth, varying in size and sound.