13. cause, reason

cause 指造成某一事實(shí)或現(xiàn)象的直接原因，后接of sth./doing sth;
reason用來(lái)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(yùn)動(dòng)，鍛煉（不可數(shù)）;
exercises練習(xí)（可數(shù)）;
practice（反復(fù)做的）練習(xí) eg:Practice makes perfect.

15. class, lesson

作"課"解時(shí),兩者可以替換.指課文用lesson;
指班級(jí)或全體學(xué)生用class. eg:lesson 6; class 5

16. speech, talk, lecture

speech指在公共場(chǎng)所所做的經(jīng)過(guò)準(zhǔn)備的較正式的演說(shuō);
talk日常生活中的一般的談話，講話;
lecture學(xué)術(shù)性的演講，講課 eg:a series of lecture on…