What causes the formation of firn ice?
A.Gravity.
B.Continual accumulation of snow.
C.Volcanic emission.
D.Snow melting.

A.Gravity.
B.Continual
B.
C.Volcanic
C.
D.Snow
D.

【参考答案】

B
解析：参考第二段第二句。firn或neve是“冰原、粒雪”之意。