What did the speaker probably talk about previously?

Up to now, we’ve focused on the positive impact of the automobile on society in the United States. Today we’ll look at some of the negative effects. A number of sociologists blame the automobile for the decline of the downtown areas of major cities. In the 1950’s and 1960’s, the automobile made it possible to work in the city and yet lived in the suburbs many miles away. Shopping patterns changed. Instead of patronizing downtown stores, people in the suburbs went to large shopping malls built in the open areas outside the cities. Where everything is cheaper. Merchants in the city failed: stores closed. Downtown shopping areas became deserted. In recent years, there has been a rebirth for a number of downtown areas, as suburbanites, especially young married couples, have moved into the city to avoid roads clogged with traffic between the suburbs and cities every morning and evening. Now let’s look at some slides that illustrate these trends. By the way, tomorrow I’ll explain the effect of all these automobiles on the environment, for example, what happens to the atmosphere as result of burning gasoline and depletion of natural resources like fossil fuels?