The bases of middle clouds are located at altitudes of between __________.

Correct Answer: Option B — 6,500 to 20,000 feet (1981 to 6096 meters)

Bowditch meteorological classifications define middle clouds, including altocumulus and altostratus, as occupying altitudes between 6,500 and 20,000 feet (1,981 to 6,096 meters) above the surface.