Mark the letter A, B, C, or D on your answer sheet...

Câu hỏi: Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.

In order to sustain a snowfall, there must be ______to feed the growing ice crystals.

A. of constant inflow of moisture

B. a constant inflow of moisture is

C. moisture constant flowed in

D. a constant inflow of moisture