From which type of clouds do hail pellets form?

The correct answer is B. Cumulonimbus.

Hail pellets form in strong thunderstorms associated with cumulonimbus clouds. These clouds have strong updrafts that carry water droplets upward into very cold areas of the atmosphere, where they freeze and fall back down, accumulating layers of ice and eventually forming hail. If you have more questions about cloud types or weather phenomena, feel free to ask!