the second is eating two cup and the third group of mice is eating three cups.
After three years,
the healthiest group is the one that is only eating one 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 two years.
Most of the mice in this group are still alive after three years.
The second group of 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 two years.
The last group of mice spends most of the days 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 two years.
17. According to the passage,
what animals are often used by scientists to learn about man?
18.What are the scientists studying in this laboratory?
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