单项选择题
Cirrus clouds are composed primarily of（）.
A.ice crystals B.water droplets C.snow crystals D.nitrogen
单项选择题 An aneroid barometer reading should be corrected for differences in（）.
单项选择题 An anemometer on a moving vessel measures（）.
单项选择题 Altocumulus clouds are defined as（）.
