QUOTE:
Originally posted by ieagle at 2007-8-23 09:59
在非英语国家，不会说本地话，希望跟对方用英语交流该怎么说？
In different contexts all can be used.
Can and could are modal verbs. In this example, the can is referring to ability. So if you said "can you speak English" you are asking "do you have the ability to speak English?" This could be shortened to “do you speak English?”
Sometimes could can be used as the past tense of can. In this example, however it can’t be used as the past tense of ability because you would be asking if someone had the ability to speak English in the past.
Could can also be used for possibility. Consequently, if you said, “could you speak English” it would imply that the other person speaks English, but for some reason he or she is speaking another language. By asking the question, you would be making a request to speak English rather than an inquiry into whether English can be spoken.