随机挑选身体健康，无疾病史的大一到大四四个年级共1200名学生，每年级各300名，男女各半。
The objects were 1200 healthy and no the disease history students, 300 for each grade who were selected randomly, boys and girls half and half.
随机挑选身体健康，无疾病史的大一到大四四个年级共1200名学生，每年级各300名，男女各半。
The objects were 1200 healthy and no the disease history students, 300 for each grade who were selected randomly, boys and girls half and half.
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