13. cause, reason

cause 指造成某一事實或現(xiàn)象的直接原因，后接of sth./doing sth;
reason用來解釋某種現(xiàn)象或結(jié)果的理由，后接for sth./doing sth. eg:the reason for being late

14. exercise, exercises, practice

exercise運動，鍛煉（不可數(shù)）;
exercises練習（可數(shù)）;
practice（反復做的）練習 eg:Practice makes perfect.

15. class, lesson

作"課"解時,兩者可以替換.指課文用lesson;
指班級或全體學生用class. eg:lesson 6; class 5

16. speech, talk, lecture

speech指在公共場所所做的經(jīng)過準備的較正式的演說;
talk日常生活中的一般的談話，講話;
lecture學術(shù)性的演講，講課 eg:a series of lecture on…