Which of the following best describes hail?

a- small ice pellets that may fall to the ground in a mixture of rain and snow in the form of a solid

b- a form of precipitation that occurs when liquid and frozen precipitation freezes in layers creating chunks

c- water droplets that collide with others to form large drops as they leave the clouds and fall toward the ground

d- solid precipitation that is formed in clouds as ice crystals that stick together in groups to form flakes and leave the clouds as flakes