could

1. I had to pay a 500 deposit to the landlord before I could move into the house.
   我得付给房东500英镑押金才能搬进房里去。
2. He had no money, nor did he know anyone he could borrow from, either.
   他没有钱，也不知道能够向谁借钱。
3. There were about 500 people there, as near as I could judge.
   那里有500人，依我看有这麽多。
4. So hard did he study that he could easily pass the examination.
   他那么努力，因而能够轻易地通过那次考试。
5. The woman said that she could not sleep without her husband's snore after 20 years of marriage.
   那位妇人说结婚20年来，听不到她丈夫的呼噜声，她就睡不着觉。
6. Always he sought someone to whom he could talk without caution.
   他一直在找一个能够随便谈谈的人。
7. I wish we could see more new programmes on television, not repeats all the time.
   我真希望我们能够看到更多新的电视节目，而不是翻来覆去的那几个老节目。
8. I can't sing now, but I could when I was young.
   现在我不会唱歌了，但我年轻的时候会。

could

v.aux.（助动词）
can的过去式
Used to indicate ability, possibility, or permission in the past:
用来表示过去的能力、可能性或允许：
例句：
I could run faster then. It could be no better at that time. Only men could go to the club in those days.
那时我能跑得更快。那时好得不能再好了。在当时，只有男人可以去俱乐部

Used with hypothetical or conditional force:
用来表推测或条件：
例句：
If we could help, we would.
如果我们能帮上忙，我们会帮的

Used to indicate tentativeness or politeness:
用于表示试探性或礼貌：
例句：
I could be wrong. Could you come over hereô
我也许错了。你能到这边来吗ô