本來以為祈使句和Ving可以這樣分，但： 1.Get up early and you won't miss it. 2.Previewing the lesson before class gives me a better idea about what the teacher is going to teach. 3.[Think] carefully before you buy a new house. 已經有buy了，think應該用thinking 後來看1.3.句，覺得before after and等連接詞前後可視為一個句子，但如果以這想法為基準，第二句Previewing the lesson 就無動詞了……？