Final answer:
Vivaldi was initially hired by the Pietà as an instructor of the violin. (Option A)
Step-by-step explanation:
Antonio Vivaldi was initially hired by the Ospedale della Pietà, a charitable institution and orphanage in Venice, Italy, as an instructor of the violin. This institution was known for its musical education program and had a renowned all-female orchestra, where Vivaldi played a significant role.
Vivaldi's association with the Pietà lasted for several years, and during his time there, he not only taught the violin but also composed a substantial amount of music, including numerous violin concertos, chamber music, and vocal works. His impact on the development of violin technique and the Baroque concerto form was substantial, and he is best known today for his violin concertos, particularly "The Four Seasons."
Therefore, the correct option is: A) Violin