In recent years, smog weather has frequently appeared in China, and air quality problems have aroused great concern of the whole society. The following figure shows four cases of vertical temperature

In recent years, smog weather has frequently appeared in China, and air quality problems have aroused great concern of the whole society. The following figure shows four cases of vertical temperature distribution. The higher the ground temperature, the greater the vertical decline rate and the stronger the convection upward movement, which is more conducive to the diffusion of pollutants. On the contrary, the decline rate is small or the temperature inversion phenomenon appears, which is not conducive to the diffusion of pollutants. As can be seen from the figure, BCD is an inversion phenomenon, so A is most conducive to the diffusion of pollutants.

So choose: a.