Glaciers form when the snow, sleet, and hail that fall in a given climatic region exceed the amount capable of being lost through evaporation or meting.
A. the snow, sleet, and hail that fall in a given climatic region exceed the amount capable of being ...[amount compared with snow, incorrect usage of plural in the verb]
B. a given climatic region's fallen snow, sleet, and hail exceeds the amount able to be ....[same as the first]
C. the amount of snow, sleet, and hail that falls in a given climatic region exceeds the amount [the parallelism here is correct: the amount is compared with the amount]
D. the snow, sleet, and hail falling in a given climatic region exceeds the amount able to be [again, snow is compared with amount]
E. a given climatic region exceeds the amount of snow, sleet, and hail that falls and cannot be [this one is obviously incorrect because the amount in the second tense is compared to a climatic region!]