GWD 11-33 C 选项

A 和 E 被讨论到爆了 所以另开一帖

这里我想问 C 为什么不好 ?  感谢 !!

Q33:

After more than four decades of research and development, a new type of jet engine is being tested that could eventually propel aircraft anywhere in the world within two hours or help boost cargoes into space at significantly lower costs than current methods permit.

A.      tested that could eventually propel aircraft anywhere in the world within two hours or help

B.      tested that could eventually have the capability of propelling aircraft anywhere in the world within two hours or to help

C.      tested, eventually able to propel aircraft anywhere in the world within two hours, or helping

D.      tested, and it eventually could propel aircraft anywhere in the world within two hours or helping

E.      tested, and it could eventually have the capability to propel aircraft anywhere in the world within two hours or help

c裡面propel 與helping並不平衡...

所以錯了~

原文中表达的是可能性，所以使用could，变换成able to就失去了原先意思的表达；

同时那个or helping只能与being tested并列，两者不可能并列的，从逻辑意思上来判断；

原文的意思是正在测试该种dd可能做什么（表达的是可能性），而不是已经做什么了。。。。

原文的意思是正在测试该种dd可能做什么（表达的是可能性），而不是已经做什么了。。。。

不过上面的看法 我不太能体会 could 和 be able to 的意义上有差别吗

我不觉得be able to 是已经做什么了   请指教!!

看来偶没说清楚呀，我说的已经做什么指的是helping如果与前面并列的话；

说说be able to与could，can的区别吧：

前者说的是一种能力：

sb is able to get 800 if he/she takes GMAT TEST: 如参加考试就能得800；

sb can get 800 if he/she takes GMAT TEST; 如参加考试，可能得200分，也可能得800分

不知道说明白了没？

关于这点我觉得很有道理 但是刚查LDOCE发现了一个奇怪的例子 请帮忙看一下

able   adjective  

1 be able to do something

a) to have the skill, strength, knowledge etc needed to do something

- I've always wanted to be able to speak Japanese.  
b)  to be in a situation in which it is possible for you to do something

- I'd like to do more gardening, but I never seem able to （这句它是归类在be able to 底下但是似乎省略了be）find the time.  

- I haven't been able to read that report yet.  

2  clever or good at doing something

- one of my more able students  

这点我也查了Longman 对于could , be able to 的差别他做了一下解释

看完之后我觉得只有时态的差别和一些词的并用而以 我觉得你讲的意思的差别 没有很大的关系

WORD CHOICE:CAN ,COULD ,BE ABLE TO

Use can and be able to to say that someone has the ability to do something.Be able to is more formal.

Use could to say that someone has the ability to do something, but does not do it. ---He could do a lot better.

Could is the past form of can. Use could or past form of be able to to say that someone had the ability to so something in the past.

In the following case, you cannot use can, you must use be able to:

with used to, to say that someone had the ability to do something in the past but no longer does-----I used to be able to play violin.

to talk about future ability. Use will be able to ----After only a few lessons, you will be able to understand basic Spanish.

After other verbs, for example might, may, would, want, or hope----He might be able to fix your car.You should be able to taste the difference.

我补充一点：象楼上说得，be able to 是不可以分开得。can 和be able to在一般得用法中似乎区别并不大，但在GMAT中区别还是比较大得，你可以去查查OG，大全之类得，有很多个这样得例子；

在保证其他语法和逻辑正确得情况下，优先选择can，这种优先性不同得例子有不同得原因，就像many of them in 和many of who be in一样，两个都是正确得，关键是GMAT喜欢用什么，不喜欢用什么，就像不用which指代前面整个句子一样，有些时候就是没有道理可言（当然了，这只是一小部分），虽然它自己也用，也许是只许州官放火，不许百姓点灯得道理吧；

这个例句确实挺奇怪的，偶查了《美国传统辞典》，根本没有这种用法。请大家继续讨论！

关于can/could 与 be able to 的区别，偶整理的针对G语法考点的区别如下，仅供参考。

不知道是否统一答案了， 不过我选 E .  

Rhetorically,  "sth is being tested and it could ... " is more consistent with the tone of " after..."

" after sth, sth is being tested ..." is unacceptable unless it is " sth is still being tested "

Logically,  " could " refers possibility.   " capability" defines ability and potentiality. Both are not the same and cannot replace each other.