1. clothes, cloth, clothing
clothes统指各种衣服，谓语动词永远是复数， cloth指布，为不可数名词 clothing 服装的总称，指一件衣服用a piece of, an article of
2. incident, aident
incident指小事件, aident指不幸的事故He as killed in the aident.
3. amount, number
amount后接不可数名词， number后接可数名词 a number of students
4. family, house, ho
ho 家，包括住处和家人，house房子，住宅，family家庭成员. My family is a happy one.
5. sound, voice, noise
sound自然界各种各样的声音，voice人的嗓音，noise噪音I hate the loud noise outside.
6. photo, picture, draing
photo用照相机拍摄的照片，picture可指相片，图片，电影片，draing画的画
Let's go and see a good picture.
7. vocabulary, ord
vocabulary词汇，一个人拥有的单词量，ord具体的单词He has a large vocabulary.
8. population, people
population人口，人数，people具体的人 China has a large population.
9. eather, climate
eather一天内具体的天气状况，climate长期的气候状况 The climate here is not good for you.
10. road, street, path, ay
road具体的公路，马路，street街道，path小路，小径，ay道路，途径
take this road; in the street, sho the ay to the museum.
11. urse, subject
urse课程(可包括多门科目)，subject科目(具体的学科)a sumr urse
12. custom, habit
custom传统风俗，习俗，也可指生活习惯，后接to do， habit生活习惯，习惯成自然，后接of doing. I've got the habit of drinking a lot.
13. cause, reason
cause 指造成某一事实或现象的直接原因，后接of sth./doing sth，reason用来解释某种现象或结果的理由，后接for sth./doing sth. the reason for being late
14. exercise, exercises, practice
exercise运动，锻炼(不可数)，exercises练习(可数)，practice(反复做的)练习
Practice makes perfect.
15. class, lesson
作"课"解时,两者可以替换.指课文用lesson. 指班级或全体学生用class. lesson 6; class 5
16. speech, talk, lecture
speech指在公共场所所做的经过准备的较正式的演说，talk日常生活中的一般的谈话，讲话，lecture学术性的演讲，讲课 a series of lecture on…
17. officer, official
officer部队的军官，official政府官员 an army officer
18. ork, job