could如果是表示“可能”用于一般过去时态时，回答可用could。Could I play the piano two years ago? 肯定回答Yes, you could.否定回答No, you couldnt.如果表示“委婉”，回答用\"can\"。
Could I have a quick word with you?
我能跟你快点儿说句话吗？
Could I have ten copies of this page, please?
请把这一页给我复印十份好吗？
Could I see you for a minute?
我能见你一下吗？
