1. I would go if I could.
能去我就去。
2. You could have been more considerate.
你本来可以更慎重些。
3. Could you do sth. for me?
你能替我做件事情吗?
4. I could run faster then.
我那时能跑得更快一些。
5. Couldn't you try it again?
你可否再试一下?
6. I could swim when I was 10.
我10岁的时候就会游泳。
7.The girl could play the piano when she was 6.
这个女孩6岁时就会弹钢琴。