May weather in Nanchang 1.

The temperature difference on April 29th is: 22- 18 = 4℃.

The temperature difference on April 30th is: 24- 18 = 6℃.

The temperature difference in May 1 day is 27- 19 = 8℃.

The temperature difference on May 2nd is: 22- 18 = 4℃.

The temperature difference on May 3rd is: 24- 19 = 5℃.

So choose C.