单词assure ,sure,ensure,insure,的区别?用法?词性?

其实,这四个单词除了词性不同,中文意思差不多,用法在一定程度上可以互换,我把各个词语用的最多的意思例举出来.
assure vt 保证,担保； 使确信；向.保证（重点使用）； 弄清楚
He hastened to assure me that there was nothing traumatic to report.
他急忙向我保证没有任何不快的事要报告.
sure adj 确信的,必定的（重点使用,用作adj）； 可靠的 adv 当然,的确
He'd never been in a class before and he was not even sure that he should have been teaching.
他以前从未讲过课,他甚至不能确定自己是否应当从事教学.
The president has never been sure which direction he wanted to go in on this issue.
这位总统从未确定在这个问题上自己想要朝哪个方向走.
ensure vt 保证,确保（重点使用）；使安全
We must ensure that all patients have access to high quality care.
我们必须确保所有的病人都能够得到高质量的护理.
insure
vt 确保,保证,给.保险（重点使用）
vi 确保,投保
For protection against unforeseen emergencies,you insure your house,your furnishings and your car.
为防止发生无法预料的紧急情况,人们给房屋、家具和汽车投保.
All the electronics in the world cannot insure people against accidents,though.
不过,世界上所有的电子设备并不能保证意外的发生.