n.对偶；相对的位置，对换（调）；换位；换质位（法）

If it is raining, then the ground is wet. Contrapositive: If the ground is not wet, then it is not raining.
如果在下雨，那么地面是湿的。逆命题：如果地面不湿，那么就没有下雨。
All dogs have four legs. Contrapositive: If an animal does not have four legs, then it is not a dog.
所有的狗都有四条腿。逆命题：如果一个动物没有四条腿，那么它就不是一只狗。
If you study hard, then you will pass the exam. Contrapositive: If you do not pass the exam, then you did not study hard.
如果你努力学习，那么你将会通过考试。逆命题：如果你没有通过考试，那么你就没有努力学习。
Every student who studies hard gets good grades. Contrapositive: If a student does not get good grades, then they did not study hard.
每个努力学习的学生都能取得好成绩。逆命题：如果一个学生没有取得好成绩，那么他就没有努力学习。
If the traffic light is red, then cars must stop. Contrapositive: If cars are not stopping, then the traffic light is not red.
如果交通灯是红色的，那么汽车必须停止。逆命题：如果汽车没有停止，那么交通灯就不是红色的。
If a person is over 18 years old, then they can vote. Contrapositive: If a person cannot vote, then they are under 18 years old.
如果一个人超过18岁，那么他们就有选举权。逆命题：如果一个人没有选举权，那么他们就不足18岁。
If a plant receives enough sunlight, then it will grow. Contrapositive: If a plant does not grow, then it did not receive enough sunlight.
如果植物得到足够的阳光，那么它就会生长。逆命题：如果植物没有生长，那么它就没有得到足够的阳光。
If a person eats too much junk food, then they will gain weight. Contrapositive: If a person does not gain weight, then they did not eat too much junk food.
如果一个人吃了太多垃圾食品，那么他们就会发胖。逆命题：如果一个人没有发胖，那么他们就没有吃太多垃圾食品。
If a computer has a virus, then it will not function properly. Contrapositive: If a computer functions properly, then it does not have a virus.
如果一台电脑有病毒，那么它就不能正常运行。逆命题：如果一台电脑能正常运行，那么它就没有病毒。
If a person is a doctor, then they have gone to medical school. Contrapositive: If a person has not gone to medical school, then they are not a doctor.
如果一个人是医生，那么他们已经上过医学院。逆命题：如果一个人没有上过医学院，那么他们就不是医生。