首先have done表示已經(jīng)做過,這點就不用談了.
can't have done 表示以前不可能做某事.
例句
---Where____Margaret have put the empty bottles?
---She________them away.They must be somewhere.
A.can;can't have thrown
B.must;must have thrown.
C.must;needn't
D.can;must throw
答案為A.第一個句子是一個疑問句而且表示可能性的推測,所以只能用情態(tài)動詞can或could,第二句的答語表示對過去的推測,所以用can't have done.
請看常見的“情態(tài)動詞 + have + 過去分詞”的用法：
一、“must + have + 過去分詞”表示對過去發(fā)生的事情或狀態(tài)進行推測,語氣比較堅定,通常只用于肯定句.如：
It must have rained last night,for the ground is wet.
You must have been mad to speak to the servant.
二、“can / could + have + 過去分詞”表示對過去某種情況的懷疑或不確定.can和could一般用于否定句和疑問句,could的語氣較can弱.如：
I didn't see her at the meeting this morning; she can't / couldn't have spoken at the meeting.
He can't have finished the work so soon.
三、“may / might + have + 過去分詞”表示對已發(fā)生的動作或存在的狀態(tài)進行不肯定的推測,might的語氣比may弱一點.這種結(jié)構(gòu)主要用于肯定句和否定句,疑問句改用can或could.如：
They may not have known it beforehand.
You might have read about it in the papers.
四、“need + have + 過去分詞”表示過去做了不必做或不需要做的事情,或過去做某事純屬多余.如：
Need they have done it last week?
I needn't have bought so much wine—only five people came.
五、“should / ought to + have + 過去分詞”表示過去本該做某事但沒做,其否定式表示過去不該做某事但做了,這種句式含有不滿或責備之意,ought to的語氣比should強一些.如：
You ought to / should have studied harder.你本應該更努力學習的.（但沒有）
He oughtn't to / shouldn't have done that.他本來就不該做那件事.（可是做了）
六、“would ＋ have ＋ 過去分詞”表示對過去的某種情況進行猜測,或本來要做某事卻因某種原因未做成,通常用來說明某一情況,但不像用should或ought to那樣含有責備之意.如：
I guess the poet would have been about twenty when she wrote her first poem.
Another worker wouldn't have acted like that.