I can't have been.不能寫成i didn't drive so fast
I can't have been.譯成：我那時不可能開那么快.（表示對過去有把握的推測）.i didn't drive so fast .譯成：我（過去）沒有把車開過那么快.（沒有推測的意思）
2課文I was doing eighty when I overtook you.不能寫成i have been driving at eighty miles an hour when i overtook you .
因為I have been driving at eighty miles an hour when i overtook you .這句話的前半句,即 I have been driving at eighty 用的是現(xiàn)在完成進行時,這個事態(tài)表示動作過去發(fā)生延續(xù)到現(xiàn)在,以至于延續(xù)到將來,因此要求有與之相匹配的表示現(xiàn)在的時間.而when i overtook you 這個時間狀語只表示過去的時間,所以句子本身又不匹配的情況.
3課文Didn't you see the speed limit?不能寫成aren't you see the speed limit .在 Didn't you see the speed limit?句子中,主語的動作時see,see是行為動詞,在轉(zhuǎn)換成問句或否定句是要用助動詞do,does,did等,而不用系動詞be,因此本句不能用aren't.
4課文 He wasn't dreaming,officer.不寫成 he didn't dream,officer .因為He wasn't dreaming,officer.如果補充完整應(yīng)是：He wasn't dreaming when you overtook us,officer.所以要用過去進行時.
5課文But you'd better not do it again!和you'd better not drive so fast next time 的句意有差別,again：再一次,又一次.next time：下一次.還有原文用do it是為了避免重復drive這個詞,所以還是不行.
6課文Thank you.I'll certainly be more careful.句中的careful是個形容詞,形容詞應(yīng)該跟在be的后面.carefully是副詞,副詞常常用來修飾動詞,形容詞和副詞.所以本句中只能用careful.certainly的位置比較靈活,可以在句首,句中,句尾.