单项选择题
An air mass is termed warm if（）.
A.it is above 70°F B.the ground over which it moves is cooler than the air C.it originated in a high pressure area D.it originated in a low pressure area
单项选择题 All of the following are associated with cumulonimbus clouds EXCEPT（）.
单项选择题 After a cold front passes，the barometric pressure（）.
单项选择题 After a cold front passes the barometric pressure usually（）.
