could / can
1)could 是past tense/ can是present tense
If you practise more,you can pass the exam (考试还没开始)
If you practised more,you could pass the exam.(考试结束罗,但没及格)
2) 建议某人可做某事,我们会讲could have (done something),can have
You could have met me at the station,couldnt you?
因为建议,是假设性的情况,所以要用 past tense的 could
3) can同could在问句中语气不同:
can是问能力 or 差不多等於命令
could是问可不可以(有礼貌)
比较:Can you fix your bed?(这是阿妈说的,不可以say no)
Can you drive?(问能力)
Could you help me on this?(问同事,有礼貌,不是命令)
4) 3.关於未来发生可能性要用could:
I could come tomorrow if you want.如果你想,我明天可以来
I can come tomorrow.我明天能够来
.
what can I eat?才是
因为你是真的生病,不是假设
而你问的时候就已现在式了...