单项选择题
If an observer in the Northern Hemisphere faces the surface wind，the center of low pressure is to his（）.
A.left，slightly behind him B.right，slightly behind him C.left，slightly in front of him D.right，slightly in front of him
单项选择题 Cyclones tend to move（）.
单项选择题 Cumulonimbus clouds can produce（）.
单项选择题 Cumulonimbus clouds are most likely to accompany a(n)（）.
