单选

Question 24 to 27 are based on the following passage.
Scientists can learn about man by studying animals, such as mice, rats and monkeys. The scientists in a laboratory areexperimenting on mice and they are studying the relationship between diet and health.
In this experiment, the scientists are studying the relationship between the amount of food the mice can eat and theirhealth. The mice are in three groups. All these groups are receiving the same healthy diet. But the amount of food that eachgroup is receiving is different. The first group is eating one cup of food each day, the second two cups, and the third threecups.

After three years, the healthiest group is the one that is only eating one cup of food each day. The mice in this group arethinner than normal mice but they are more active. Most of the day, they are running, playing with one another, and using theequipme
A.they run and play all day long
B.they eat only one cup of food a day
C.they live longer than the other groups
D.they are bored with the kind of food in the cup

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