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73.Cohmbining enormous physical strength with higher intelligence, the Neanderthals appear as equipped for facing any obstacle he environment could put in their path, but their relatively sudden disappearance during the Paleolithic era indicates that an inability to adapt to some environmental change led to their extinction. A. Appear as equipped for facing any obstacle the environment could put in their path, B. Appear to have been equipped to face any obstacle the environment could put in their path, C. Appear as equipped to face any obstacle the environment could put in their path, D. D appeared as quipped to face any obstacle the environment could put in their paths, E. Appeared to have been equipped for facing any obstacle the environment could put in their path, 我选的是C，正确答案是B，OG后面解释是because Neanderthals ''disapeared,'' the verb describingtheir apparent abilitied cannot be present tense, so as equipped myst be changed to to have been equipped. 这里我看不明白，为什么要改写成现在完成时被动态来修饰？请各位高手指教 -- by 会员 阿尔法柔笼 (2010/6/9 18:20:45)
There is more than one difference between the simple past and the present perfect. The simplest difference is the grammatical difference that the simple past can be used with expressions which signify a definite, particular time in the past.
I wrote a letter yesterday.
I wrote a letter at 7 o'clock.
I wrote a letter last Monday.
I wrote a letter several weeks ago.
The present perfect cannot be used with such expressions. (After all, it IS a "present" tense!)
I have written a letter yesterday. (wrong!)
I have written a letter at 7 o'clock. (wrong!)
I have written a letter last Monday. (wrong!)
I have written a letter several weeks ago. (wrong!)
Being a "present" tense, the present perfect can be used with "now":
I have now written a letter.
Another difference is the way the two tenses "cut through time".Imagine time as a very, very long loaf of bread extending into infinityfrom where you are located. As you look into the distance at this long loaf of bread, let's say that you are looking into the past. The loaf ends at your feet and this is the present moment.
When the simple past tense is used to report an event, it "cuts a slice out of time". To do this, somewhere along the bread loaf(time) you make two cuts, fairly close together. The cuts represent thebeginning and the end of the event or action. Suppose you wrotea letter. It took, let's say, an hour. Then the thickness of the bread slicerepresents one hour of writing. If that hour took place this morning,the slice is located quite close to you: "I wrotea letter this morning". If that hour took place yesterday, the slice is located farther from you: "I wrote a letteryesterday." If it took only 15 minutes to write the letter, the breadslice is much thinner, but again the slice may be closer to or fartherfromthe present (e.g., this morning or yesterday).
When the present perfect tense is used to report an event, the"slicing" is different, because you don't know exactly where the sliceis located along the loaf. If you say "I have writtena letter ", youknow there were two cuts in the loaf to make the slice, but you don'tknow where. You only know that if you examine the loaf, you willdiscover a slice representing the letter writing somewhere along the loaf. Another feature of the present perfect is that you can limithow far back in time - how far back along the loaf - you want to go inyour search. This is done with a "since" clause. In the sentence "SinceMonday, I have writtena letter", we know that the slice representing the letter writing will be found between the distance from us which represents Monday and the present moment (at our feet). But we still don't know exactly where within that more limited part of the loaf we will find the slice.
Another way to look at it is that the simple past "singularizes","individuates", or "particularizes" an action by focusing on a specifictime. Whether the specific time is mentioned or not, thesimple past ,when used to report an event, always implies "at a certain time". Infact, it is this implication that particularizes the event. Even if theimplication is "when it happened", the implication is still there. "Didyou see that?" implies "Did you see that when it happened?" Anotherexample: "Did you notice that John got nervous when we mentioned the missing cash?"The noticing we are referring to is the noticing of that specificinstance of nervousness that occurred at the time we mentioned themissing cash.
The present perfect, however, does not "singularize", "individuate" or "particularize" an action. With the present perfect, we don't even know exactly when the action happened! What is more important with the present perfect is that the action now has some felt effect on the present. When you say "I have written a letter",in a way you are pointing to that letter and saying, "And here it is.Here is the letter I have written" -- even though the pointing andsaying may be only a mental pointing and saying! The important thing ishaving (hence the auxiliary "have") the letter now.
Another way to look at the present perfect is that it is the "diarytense". It is as if everyone has an imaginary diary where his lifeexperiences are written. With "I have writtena letter" we are saying that we will find in your "diary" today, - if we look now - the notation: "Letter - written!" on some page of the "diary", but we don't know or don't care which page that might be.
Becoming adept at the use of the simple past and the present perfect takes lots of practice. Don't be too disappointed if you find it difficult at first.  |
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发表于 2010-6-9 18:20:45
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