Clouds appearing in the following order：cirrus， cirrostratus， altostratus， stratus， and nimbostratus usually indicate the approach of a（n）（）.

Clouds appearing in the following order：cirrus， cirrostratus， altostratus， stratus， and nimbostratus usually indicate the approach of a（n）（）.
A.warm front
B.occluded front
C.medium front
D.cold front
正确答案：warm front