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：
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：
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：
I could be wrong.Could you come over here?
我也许错了.你能到这边来吗?
sure
adj.确信的；可靠的；必定的
adv.当然；的确
sure做形容词,be sure of 对什么肯定的意思
在句中作表语
eg:i,m sure of that
sure做副词,be sure to do sth 不要忘了做某事的意思
eg:be sure to close the window 这是一个命令语气.
could和sure的用法：
could
aux.
“can”的过去式; 能够，打算; 用于假设语气的条件句; 用于虚拟语气的结论句;
双语对照：
1.He could have made a fortune as a lawyer.
他本可以当律师挣大钱的。
2.You could have been killed!
你差点儿就没命了！
3.He did not regret saying what he did but felt that he could have expressed it differently.
他并不后悔说了自己所做的事，但觉得本可以换一种方式表达。
sure
adj.确信的，确实的; 有把握的; 无疑的; 一定的;
adv.当然; 确实地; 无疑地;
双语对照
1.He'd never been in a class before and he was not even sure that he should have been teaching.
他以前从未教过课，甚至不确定自己该不该教课。
2.Pretty sure it 's the latter.
当然是后者了。
3.The president has never been sure which direction he wanted to go in on this issue.
总统一直都不确定自己想从哪个方面来着手处理该问题。
标签：could,sure,用法
