句首不定詞（to V）、動名詞 （Ving）和原形動詞(V)的使用時機
(一) 連接詞連接兩個子句，應為祈使句，句首為原形動詞(V)。 連接詞and ：Walk fast and you can catch the first train. 走快一點，而你就可以搭上第一班公車。 連接詞or : Walk fast or you will be late. 連接詞before: Turn off the light before you go to bed.
(一)句首原形動詞(V)的使用時機 連接詞when: Remember to lock the door when you leave the house. 連接詞if : Tell John to call me if he comes to the office. 連接詞because: Leave Mary alone now because she just had a bad day.
(一)句首原形動詞(V)的使用時機 連接詞although : Forgive Peter although he cheated on you. 連接詞after : Check the answers after you finish the test.
(二) 無連接詞連接時，表示是單句， 句首為不定詞（to V）、動名詞（Ving）當主詞，可互換 1. Living in a big city is convenient. （住在大城市是方便的。） =To live in a big city is convenient.
(二)句首為不定詞（to V）、動名詞（Ving）當主詞，可互換的使用時機 2. Previewing the lessons is important in learning. =To preview the lessons is important in learning.
(二)句首為不定詞（to V）、動名詞（Ving）當主詞，可互換的使用時機 3. Having the right career will surely make one happier. =To have the right career will surely make one Happier.
(三) 無連接詞連接，表示是單句，句首且有逗點時，句首應為不定詞（to V） 表示目的，中文為「為了要…」，不可以和動名詞（Ving）代換。 To buy a new house, they work day and night every day. （為了要買一間新房子，他們每天日以繼夜地工作。）
(三)無連接詞連接，表示是單句，句首且有逗點時，句首應為不定詞（to V）,且不可以和動名詞（Ving）代換的使用時機。 To choose the right career, you must understand yourself first.
(三)無連接詞連接，表示是單句，句首且有逗點時，句首應為不定詞（to V）,且不可以和動名詞（Ving）代換的使用時機。 To get a better grade, you need to study hard.
練習1 1. (read) good books is good for you. Reading /To read
練習2 2. (go) away because I don’t want to see you again. Go
練習3 3. (choose) the right career, you must understand yourself first. To Choose
練習4 ( dance) well and you will win the first prize in a dancing contest. Dance
練習5 ( not be) angry when he does the worst on the test. Don’t be
Good Bye