Read the Following Scenario and Answer the Question Below

Read the following scenario and answer the question below.
Thousands of young families moved ʺover the hillsʺ and into the San Fernando Valley, a suburb of Los Angeles, after World War II. New neighborhoods were springing up, replacing orange groves and open space; roads and schools quickly sprang into existence, trying to keep pace with the rapid population growth. Ringed by beautiful mountains, the entire Los Angeles basin looked like a new, green, sun-filled paradise to the families seeking a fresh start. In the early 1950s, one of the common family chores in Los Angeles was to carry the trash out to the stone incinerator behind the garage where each family burned all of their dry trash. ʺWetʺ garbage was collected and taken to a city dump, where it was burned by the city. Everyone throughout the city either used an incinerator or burned things in an open trash pile; there were over 400,000 backyard trash incinerators. On warm afternoons, eyes would sometimes sting and burn. People would stop, close their eyes, and let the cleansing tears refresh irritated eyes. They accepted this as a normal part of life in sunny California.
-In the mid-1950s, a researcher in Los Angeles was able to create smog by setting up a large, clear chamber and using it to expose auto exhaust to sunlight. He was demonstrating _________________

A) photochemical reactions
B) point source pollution
C) non-point source pollution
D) the cause of acidic deposition
E) the cause of ozone depletion