“It’s+adj.+for+sb.+不定式”表示“做某事对某人来说怎么样”.常用于表示事物的特征特点,表示客观形式的形容词.若形容词是描述做的事情（即adj描述的是to do）,不是对不定式行为者的品格进行评价,用for sb.这类形容词有:
important(重要的),necessary(必要的),
difficult(困难的),easy(容易的),
hard(艰难的),dangerous(危险的),
safe(安全的),useful(有益的),
pleasant(舒适的),interesting(有趣的),
impossible(不可能的),
right(正确的) likely(可能的)等，例如:
It’s not easy for them to learn a foreign language.(=To learn a foreign language is not easy for them.)
对于他们来说学好一门外语不容易.
It's very hard for him to study two languages(=To study two languages is very hard for him).
对他来说学两门外语是很难的.
It’s very important for students to listen to teachers carefully.(=To listen to teachers carefully is very important for students.)对于学生来说上课认真听老师讲课是非常重要的.
It’s necessary for us to get to school on time.(=To get to school on time is necessary for us.)
对于我们来说按时到校是非常必要的.
It’s important for her to come to the party.=It is important that she should come to the party.
对她来说来参加聚会很重要.
It’s very dangerous for children to cross the busy street.对孩子们来说,穿过繁忙的街道很危险.
It’s difficult for us to finish the work. 对我们来说,完成这项工作很困难.
to+动词原形，构成动词不定式，在这句话中充当真正主语，it只是形式主语。
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