It shows that the causes of weather change may be (a), cold front transit B, warm front transit C, cyclone transit D and anticyclone transit.

Test center: Frontal system and weather topic: Analysis: When a warm front crosses the border, it often brings continuous precipitation. After crossing the border, the warm air mass controlled the area, and the temperature rose, the air pressure dropped and the weather turned fine. Looking at the map, from 5th to 9th, it changed from cloudy to rainy and then cloudy. Due to the weakening and heat preservation of clouds, the daily temperature difference decreased, and the temperature rose (to 18) after the weather system transited. The maximum temperature rises to 23℃, the minimum temperature rises to 1 1℃), and the weather turns fine, so the weather system is a warm front. Therefore, choose: B. Comments: This topic is called basic topic, and the key is to read the picture correctly and get useful information.