When Dr. Robert Metcalf first used a solar cooker, the future changed for millions of Africans. He knew that billions of poor people around the world depend on the use of wood for cooking. As they take more and more firewood from wild areas. They are destroying habitats around the world. Wood collection is one reason why many animals have become endangered. But sunshine can be an alternative to fire. Dr. Metcalf says. Since his first solar cooked meal, he has helped people around the world to use simple new technologies to cook their food. Each morning in villages across East Africa, small children and their mothers wake up and walk several miles to collect firewood to cook their food. It takes much of the day, and the heavy firewood they carry home on their heads lasts only a few days. This is why Dr. Metcalf spends each summer in Africa. He teaches women and children in villages how to cook with the sun. So far, more than thirty thousand African families now have solar cookers, and new programs will introduce solar cookers to millions of families. To find water, women and children may have to walk long distance to dig holes in dry riverbeds or to gather water from streams and shallow wells. They fill their buckets（桶）and carry them home on their heads. The buckets often weigh as much as forty pounds. Not only is finding water hard work, but the water is often polluted with germs（细菌）that make people sick. Dr. Metcalf and others developed a simple，reusable tool that people can use to make sure their water is safe to drink．The tool is calked a WAPI，which stands for Water Pasteurization Indicator. The pasteurization process is named after Louis Pasteur，who developed it in the 1800s. 1．Why did Metcalf help Africans use solar cookers?