首先要理解和掌握的是be sure to do sth.用在祈使句中，不是表示判断，而是表示对对方的要求，意为"务必要"，"一定要"。例如：Be sure not to forget it！千万别忘记呀！
Be sure to write and give me all the news.
务必写信告诉我所有的消息。
Be sure to come. Don't let me down.
你一定来，可别拆我的台。
Be sure to store them carefully as they bruise easily.
小心存放，因为它们很容易被碰伤。
Be sure to do the sowing in good time.
确保适时播种。
Be sure to select firm, unblemished fruit.
一定要选坚实、无疤痕的果子。
Be sure to make it clear and concise and avoid long-windedness.
注意简明扼要，反对长篇大论。
由be sure构成的句型有：
1.be sure＋of/about+动名词或名词，意为"确信......"；"对......有把握"。例如： He is sure of success. 他自信会成功的。
但是如果后面要接反身代词时，则只能用be sure of，即be sure of oneself，意为"有自信心"。例如：Joan will have an examination next week, but she is not sure of herself. 琼下周要参加一个考试，但她对自己没有十分把握。
2.be sure+不定式，意为"必定"、"必然会"、"准会"。例如：
He is sure to come tomorrow.
他明天保险会来。
It's definite that he'll come.; He is sure to come.
他肯定会来。
She is sure to come.
她一准来。
Anyone who goes food shopping without a list is sure to forget thethings they really need.
任何人如果采购食物时没列清单的话，肯定会忘了真正需要的东西。
If you make a threat be sure to carry it out if he errs again.
如果你作出威胁，在他再犯错时，一定要说到做到。
With over 80 beaches to choose from, you are sure to find a place to lay your towel
有80多个海滩可供选择，你一定能找到一处满意的。
This is sure to be an item on the agenda next week
这一定会成为下星期议事日程上的一项议题。
It is sure to rain. 天一定会下雨。
This year's harvest is sure to be good.
今年的收成错不了。
3.be sure+宾语从句，意为"确信某事一定会......"。
例如：I'm not sure whether I've met him before. 我不能确定以前是否见到过他
I am not sure whether I was knocked over by the blast or whether I just fell
我拿不准自己是被爆炸的气浪掀翻的还是恰巧跌了一跤。
You'd better reckon without me, as I am not sure whether I shall be able to be present.
你最好别把我算进去，因为我能否出席还不一定。
I'm not sure whether I can win or not.
能不能赢，我心里没底。
We were not altogether sure that the comet would miss the Earth
我们不能完全肯定彗星不会与地球相撞。
I am not sure that this is sound democratic practice
我不能肯定这是正确的民主行为。
Confidentially, I am not sure that it wasn't above their heads.
私底下说，我不敢肯定他们明白了。
You can be sure that our team will win.
我们队准保胜利。
4. make sure tha+从句，表示确保……确认……，确信……；一定要认真……
We could use pressure to make sure that Syria doesn't play the roleof spoiler in the region.
我们可以施加压力来确保叙利亚不在该地区扮演破坏分子的角色。
You've got to make sure that people work together across disciplines
你必须确保让那些出身不同学科的人一起共事。
He looked in the bathroom to make sure that he was alone
他往浴室里看了看，确定就他一个人。
If you have something to say make sure that it is accurate, succinctand to the point.
在阐述观点时一定要准确、简洁、中肯。
Make sure that the firm's insurance cover is adequate.
确保该公司上了足够的保险。
Make sure that all gas fires and central heating boilers are servicedannually.
确保所有的煤气取暖器和中央供暖的锅炉每年都检修一次。
Make sure that you follow the instructions carefully
一定要认真按照操作指南来做。
Before you cut the cloth, make sure that the pattern matches up on both edges.
在裁剪布料前要确保两个边缘的图案对称。
Make sure that you drink plenty of fluids.
务必保证足够的水分摄入。
Joseph made sure that he was never palmed off with inferior stuff.
约瑟夫确保自己从不会被骗买一些次等原料。
They made sure that he died a horrible death
他们让他死得很惨。
Make sure that you do not pierce the skin when boning the chickenthighs
剔鸡腿骨时切勿戳破外面的皮。