问题
There are so many foggy days these years. We all wonder ______________________.
A:what can we do to prevent it
B:what we can do to prevent it
C:how can we do to prevent it
D:how we can do to prevent it;
B:what we can do to prevent it
C:how can we do to prevent it
D:how we can do to prevent it;
正确答案是：
