could 和 can 到底什么关系

huangsiyan

could 和 can到底什么关系 能随时互换么？比如这道题 全部是现在时，为什么用了could，我记得以前做过题说could是can的过去式 不能使用
Even though sub-Saharan Africa often evokes images of drought and famine, researchers say that the area is the home of more than 2,000 grains, vegetables, roots, fruits, and other foods that have the possibility for feeding the continent, even other parts of the world.
(A) have the possibility for feeding the continent, even
(B) have the possibility of feeding the continent, even of
(C) could feed the continent, so even with
(D) could feed the continent and even
(E) could possibly feed the continent and, in addition, for even

judyenglishS

印象里在GMAT里面只考时态上的区别。因为语气上的区别不大，基本不能作为绝对排除因素。也就是说could可以用于现在，也可以用于过去，而can只能用于现在。

huangsiyan

有can与could同时存在时要注意时态。could很多时候是can的过去式。不过具体问题具体分析，这道题主语是物， ...
sbjqbS 发表于 2011-1-10 21:32

    谢谢回答！！！
可是没太懂 什么叫两者是物用could 两者是人就用can 么？ 这句话不对么 鸟巢 can be a good place to visit  一定要用could么？

sbjqbS

有can与could同时存在时要注意时态。could很多时候是can的过去式。不过具体问题具体分析，这道题主语是物，两者相比应该用could

liexodus

此处could表虚拟?