According to the passage, what animals are often used by scientists to learn about man?

One way that scientists can learn about man is by animals, such as mice, rats and monkeys. The scientists in this laboratory are experimenting on mice. They are studying the relationship between diet and health. At this time over 100 experiments are going on in this laboratory. In this experiment, the scientists are studying the relationship between the mount of food the mice eat and their health. The mice are in 3 groups. All the 3 groups are receiving the same healthy diet. But the amount of food that each group is receiving is different. The first group is eating I cup of food each day, the second is eating 2 cups, and the third group of mice is eating 3 cups. After 3 years, the healthiest group is the one that is only eating I cup of food each day. The mice in this group are thinner than normal mice. But they are more active. Also they are living longer. Mice usually live for 2 years. Most of the mice in this group are still alive after 3 years. The second group of mice is normal weight. They are healthy, too. They are active, but not as active as the thinner mice. But they are only living about 2 years. The last group of mice spend most of the day eating or sleeping. They are not very active. These mice are living longer than the scientists thought: about a year and a half. But they are not healthy. The experiment is still going on. The scientists hope to finish their studies in 2 years.