1. rational, reasonable

rational a. 理性的，区别于无理性；理智的，区别于感情用事的。

The rational thing to do was to take the sick man to a doctor.

理智的做法是送病人去看医生。

reasonable a. 有道理的，公平合理的，或指人讲道理的。

That man works very hard, so it is reasonable for him to ask for more money.

那个人工作努力，所以他要求加薪是合情合理的。

2. refrain, restrain, constrain

refrain v. 抑制，禁止，强调抑制一种冲动，是正式用语，为不及物动词，后接介词from。

Students refrain from smoking in the classroom.

学生们克制住不在教室抽烟。

restrain v. 抑制，约束，指通过管束阻止某事发生，是及物动词，其习惯用法是restrain sb. (sth.) from doing。

She restrains her dog by walking him on a leash.

溜狗时，她牵着狗来限制它的活动。

constrain v. 强迫，力劝，是及物动词。

A law constrains the government from spending more money than it takes in.

法律限制政府开支大于收入。

3. respectable, respectful, respective一组形近易混词。

respectable a. 值得尊敬的，有好名声的。

They are respectable people who are liked and trusted in their town.

他们在家乡是受人们敬爱和信任的人。

respectful a. 尊敬他人的，恭敬的。

Students and teachers should have a respectful attitude toward each other.

师生应该相互彬彬有礼。

respective a.单个的，分别的。

4. revolve, evolve, involve

revolve v. 旋转，转动。

The room began to revolve , then he fainted.

屋子开始旋转，然后他就昏倒了。

evolve v. 发展，演变。

Agriculture evolved slowly over thousands of years.

几千年来，农业发展得很缓慢。

involve v. 需要，包含；使卷入，牵涉。

Getting a driver's license involves learning how to drive, studying the rules of the road, and taking a test.

要得到驾驶执照需要学习开车，学习交通规则，还要经过考试。

5. sanction, sanitation

sanction n. 认可，准许，批准。

I need my parents' sanction to stay out late.

我晚回家需要得到父母的批准。

sanitation n. 公共卫生，环境卫生，卫生设备。

Strict sanitation is used in businesses such as barber shops and restaurants.

在理发店和餐馆等营业场所执行严格的公共卫生制度。