Hail/snow is a precipitation form which results when water vapour condenses directly into a solid state forming tiny crystals

Snow is precipitation that falls in the form of ice crystals. Hail is also ice, but hailstones are just collections of frozen water droplets. Snow has a complex structure. The ice crystals are formed individually in clouds, but when they fall, they stick together in clusters of snowflakes.

i'm sure the answer you are looking for would be

a. an ice age

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