Read the Following Scenario and Answer the Question Below

Read the following scenario and answer the question below.
Thousands of young families moved "over the hills" 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. "Wet" 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.
-Which of the following is the chief cause of industrialsmog?

A) indoor air pollution
B) generation of nuclear power
C) burning trash
D) burning fossil fuels
E) fires for heating food