A、The rising price of gas. B、People’s concern for air pollution. C、The growth of bicycle production. D、The high quality of bicyc

In the past few years, millions of Americans have become suddenly enthusiastic about the bicycle as if it were a great new invention. Annual bicycle sales doubled between 1960 and 1970, and there are nearly 70 million bicycles in the United States today.
    Of course, the bicycle has been around for more than 160 years and this isn’t America’s first bicycle passion. A wave of bicycle enthusiasm swept the land in the late 1800s and bicycle production was up to two million in 18917. Then with the coming of the automobile, bicycle declined, and for decades remained popular only with children and a few adults.
    Now, a national concern with air pollution and physical fitness has brought the bicycle back to the forefront, particularly with adults. More than eight million bikes were sold in the United States last year, a third of which bought by adults. But the year before, only 15 percent of new bicycle sales were for adults.