Wang Hua saw a "No Smoking" sign on the wall of the gas station. From this, he made the following guess about the role of smoking in the fire, which is reasonable.

A, smoking will not produce oxygen, so A is wrong;

B, the gasoline at the gas station has a low ignition point, which is flammable and not provided by smoking, so B is wrong;

C, the ignition point of gasoline is certain, smoking will not increase the ignition point of gasoline, so C is wrong;

D, smoking can produce heat, make the gasoline temperature rise, reach the ignition point, so D is correct.

So choose D.