Look at the vertical temperature distribution map below, in which () A.B.C.D is most conducive to the diffusion of pollutants in haze weather.

The higher the ground temperature, the greater the vertical decline rate and the stronger the convection upward movement, that is, the temperature decreases with the increase of height, which is more conducive to the diffusion of pollutants. On the contrary, the smaller the decline rate or the inversion phenomenon is, the more unfavorable it is to the diffusion of pollutants. As can be seen from the figure, BCD is not conducive to the diffusion of pollutants because of the inversion phenomenon, while the temperature in A decreases with the increase of height, which is most conducive to the diffusion of pollutants.

So choose: a.