In the 1870s由听力材料的第一句可知。

In the 1870s, people began to ride a new kind of bike called the Ordinary. The Ordinary, however, was an unusual bike. For one thing its wheels were of different sizes. The front wheel was four to five feet high, while the back wheel was about a foot and a half high. Because its front wheel was so large, the new bike was faster and quieter. What is more, the rider’s body was not bumped around as much on the Ordinary. But the Ordinary wasn’t comfortable for anyone. It was so high that getting on and off was very difficult. As years passed, other ways of making a fast, light bicycle were discovered. And.by the end of the 1900s, the Ordinary was just about gone.