Reаd the fоllоwing scenаriо аnd answer the questions 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; many roads and schools were quickly built in an effort to keep pace with the rapid population growth. This rapid growth also meant that many of these families relied on automobiles to get around the new expanding area. 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 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 their irritated eyes. They accepted this as a normal part of life in sunny California.In the 1950s, Los Angeles became famous for its smog. Which of the following contributed to the smog problem?