be about to对be sure的用法常感困惑不解，现将其主要用法归纳如下。
1. be sure+of/ about+动名词或名词，意为确...... .....有把握”。但在接名词时，be sure of侧重指主语对某抽象事物的确信无疑:而be sure about则侧重指主语对某具体事物的确信无疑。例如:
He is sure of success.他自信会成功的。
I'm sure of his honesty.我肯定他是诚实的。
However, he went on to explain that he was not sure about two things- thegrammar and some of the
idioms.不过，他接着就解释说，他在语法和某些习惯用语方面都没多大把握。
If you are not sure about the situation in the world, you can read the newspaper every day.如果你对世界形势不大了解，你可以每天看看报纸。
若后面要接反身代词，则只能用be sure of,即be sure of oneself，意为“有自信心"。例如:
Joan will sit for an important examination next week, but she is not sure of herself,琼下周要参加一个重要考试，但她对自已没有十分把握。
2. be sure+不定式，表示说话人对句子主语作出的判断，认为句子主语“必定”、“必然会”、“准会”。例如:
Itis sure torain.天一定会下雨。
He is sure to have known about that.他准会知道那件事。
He told me I was sure to get a warm welcome.他告诉我，说我准会受到热情接待的。
然而be sure to do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 send my regards to your mother.务必代我问候你母亲。
Be sure not to do that again.一定不要再干那种事了。
3. be sure+宾语从句， 表示主句主语对宾语从句中涉及的事物所作出的判断，意为"确信某事一..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。
We are sure he will make great progress this term.我们确信他这学期一定会取得巨大进步。

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