In autumn, there are frequent haze weather in northern China, and PM2.5 particulate matter is the chief culprit of haze formation, which has aroused public concern about the rising PM2.5 index.

(1) smog can increase a large number of inhalable particles in the air;

(2) Among the three masks for this problem, the third mask is light in weight and high in technology. The function of the mask is to filter out inhalable particles in the air, so the filtration is not necessarily solid-liquid separation;

(3) A. Carbon dioxide and water are rich in energy. If this technology is successful, it can alleviate the energy crisis facing the world;

B as can be seen from the figure, the reaction products of carbon dioxide and hydrogen under the composite catalyst include liquefied petroleum gas, gasoline, methanol, etc. , belonging to the mixture.

C, according to the transformation relationship between substances in the figure, there is a recyclable substance in the system, namely carbon dioxide.

So, the answer is: (1) d; (2) (3) filtration is not necessarily to separate insoluble solids from the liquid; (3)ABC；