...may as well ... as ...
結構︰may/might as well+原形動詞 A+as+原形動詞 B
說明︰此句型意為“與其 B 倒不如 A”。相當於“had better A than B”。“may as well ... as”實現的可能性較大，而“might as well ... as”實現的可能性較小。
Since it is raining hard, you may as well stay here as leave.
既然雨下得這麼大，你與其離開倒不如待在這兒。
You might as well throw your money into the sea as lend it to him.
你借他錢不如把錢扔到海裡去。
You might as well not know a thing at all as know it only a little.
只知道一點點，不如完全不曉得。
I may as well die as marry him.我與其嫁給他，倒不如去死算了。(我若嫁給他，很可能去死。)
I might as well die as marry him.
我與其嫁給他，倒不如去死算了。(我不太可能嫁給他，也不太可能去死。)
You might as well talk to a stone as try to argue with a stubborn woman.
你與其跟一個倔女人爭吵，還不如對一塊石頭說話。
You might as well advise me to give up my fortune as my argument.
你勸我停止辯論，倒不如勸我拋棄一切財產。
You might as well ask the tree for help as request him to reduce the price.
你與其要他減價還不如求助於一棵樹。
... must have V-ed ...
結構︰主詞+must have+過去分詞…
說明︰此句型意為“一定曾經…”。本<句型>是對過去之事做肯定之推測，而“must+原形<動詞>”是對目前或將來之事做推測。
Anyway, he must have eaten a lot because now he is fat.
無論如何，他一定吃了很多東西，因為現在他胖了。
You must have mistaken her for her sister. 你一定是把她誤認為是她的姊妹了。
They must have left. 他們一定是離開了。
The rubbing must have worked. 搓揉一定是有效了。
They must have read the article. 他們一定讀過這篇文章。
You must have seen him before. 你以前一定見過他。
He must have forgotten my name. 他一定忘了我的名字。
He must have told you about it. 他一定告訴過你這件事。
Tom must have taken your dictionary by mistake. 湯姆一定是弄錯了才拿了你的字典。
The poet must have been very young when he wrote this poem.詩人寫這首詩時一定非常年輕。
... may have V-ed ...
結構︰主詞+may/might have+過去分詞
說明︰此句型意為“很可能曾經…”。表示對過去之事做不太肯定的推測。而“may/might+原形<動詞>”是對現在或未來事物做推測。might have 所表示的可能性要比 may have 低一些。
He may have overslept this morning. 今天早上他或許睡過頭了。
The tea is hot; he may have been here before. 茶還熱著，不久前他很可能在這裡。
He may have known the truth; otherwise he wouldn’t be so angry now.
他當時很可能知道事情的真相，否則他不會這麼生氣。
The boy might have known the truth, but I am not quite sure.
這男孩當時也許知道真相，但我不很確定。
... cannot have V-ed ...
結構︰主詞+cannot have+過去分詞
說明︰此句型意為“不可能曾經…”。是對過去之事做否定的推論，此時一定要用 cannot have 或 cannot，不能使用 must not have 或 must not。而“cannot+原形<動詞>”是對目前或將來之事做否定的推論。
She cannot have written the letter herself. 這封信不可能是她自己寫的。
He is honest, so he cannot have stolen my money.他是個老實人，所以他不可能偷了我的錢。
He cannot have caught a cold, because I saw him dancing with Mary the same day.
他不可能感冒，因為當天我還看到他跟瑪麗跳舞。
... would have V-ed ...
結構︰主詞+would have+過去分詞
說明︰此句型意為“原本會…但卻未如此”。用以表示“與過去事實相反”的<假設語氣>。
He would have attended meeting, but upon learning that he had no time, he dropped the idea.
他原本要出席會議的，但知道沒有時間，就打消了這個念頭。
I would have told you the truth, but you didn’t give me a chance.
我本來要告訴你事情的真相，但是你不給我機會。
I would have done it, but I had no time. 我本來要辦這事的，可是沒時間。
She would have married him, but when she learned that he was a rascal, she parted with him.
她本來會嫁給他的，但知道他是個流氓後，她就離開他了。