Thousands of years ago, people didn’t live in cold places because they didn’t know how to keep themselves warm. Later they learned to make clothes. When an animal was killed, they made use of its skins to cover their bodies.     19    .

Nature is people’s good friend. It once helped people find fire, when lighting hit a forest and started a fire.     20    . The fire kept them warm, and also frightened wild animals. Soon people found the food cooked tasted much better, so they began to use the fire to cook food.

    21     . When they got a fire from the forest, they tried to keep it burning. If it went out, they had to wait for years.

    22    . For example, they made fire by boring wood or knocking two pieces of stones.

Today it’s easy for people to make fire because they have matches, lighters and different kinds of heaters.     23    

The Boston Marathon is one of the world's oldest and most famous races. The first Boston Marathon began in 1897.

In 1966,a woman named Gibb took part in the Boston Marathon and finished ahead of most of the men.

Gibb first saw and got to know the Boston Marathon in 1964. And she wanted to run the race herself. For nearly two years, Gibb trained hard to prepare for the race. But when she sent in an application（申请）for the 1966 race, she was refused.

At the time, the longest official races for women were only 1. 5 miles. Many people didn't think women were able to run longer than that. But the 23-year-old Gibb didn't give up her dream. She came up with a plan to run the race anyway.

On April 19, she showed up at the marathon. She wore her brother's shorts and a sweatshirt to disguise that she was a woman.

Gibb hid near the starting line. When the race began, she jumped into the crowd. Shortly into the race, Gibb took off her sweatshirt. To her surprise, the crowd cheered when they realized she was a woman. Gibb finished the race in 3 hours and 21 minutes-faster than two thirds of the men.

In the years that followed, she and other women ran in the Boston Marathon, even though the rules still stopped women from running in the race. Finally, in 1972,the marathon was officially opened to women.