问题
In the past few years, so many areas throughout the world have been hit by such destructive earthquakes, snowstorms and tsunamis ________ we have never experienced before, ________ makes us worried a lot about nature disasters.
A:that; that
B:as; which
C:which; it
D:when; as
B:as; which
C:which; it
D:when; as
正确答案是：
