用单词can、could分别造个句子

I can play the piano.
我会弹钢琴.

He could count numbers at the age of three.
他三岁时就会数数了.

I could have finished it.
我本可以完成的.(但由于种种原因最终未完成.)

can you tell me your name?could you please close door?

could是can的过去式,在疑问词的时候是比could更委婉的问法

I can swim.我能游泳(现在式)
I could swim.我以前能游泳.(过去式,现在不知道能不能游泳)

Can you help me? 你能帮助我么?
Could you help me?(更委婉更有礼貌的问法)

could比can多一种用法:
could have done 本可以做某事

I could have gong.我本可以去的(但是因为种种原因没有去成)

1. I can ride a bike. 2. Could you help me? 那句话的意思是“我可以看见那架飞机，可我看不见一只鸟。”