What's the weather like here in the heating regiment?

A, the temperature drop in Hangzhou indicates that Hangzhou will be affected by cold air mass, and option A is wrong;

B, the chart can't reflect whether the air in Hangzhou is clean, and option B is wrong;

C, the cold front weather precipitation is mainly caused by the rise of the warm air mass, which has nothing to do with the drying of the cold air mass precipitation, and the C option is wrong;

D, there is no precipitation in the cold front weather, so it can be judged that the warm air mass has less water vapor and is relatively dry, and the D option is correct;

Therefore, choose: d.