答案为A ,你也可以展开一下学习,这种句式的用法
形式主语 it 可在下列情况下用来代替动词不定式：
1. It is + adj. （ +for sb. / sth. ） +to do sth. 常用于此句式的形容词有： easy, hard, difficult, possible, impossible, important, necessary, good, bad, exciting, interesting, surprising 等.例如：
It is easy for you to find the house.[!--empirenews.page--]
你很容易找到那座房子.
2. It is +n. （ +for sb. / sth. ） + to do sth. 常用于此句式的名词有： pity, shame, pleasure, one's duty, one's job, fun, joy, good manners, bad manners 等.例如：
It is bad manners for the young to take up the seats for the old.
年轻人占有老年人的专用座位是不礼貌的.
3. It is + adj. + of sb. + to do sth. 此句式中的形容词主要用来描述某人的品德、特征.常用于该句式的形容词有： kind, nice, wise, silly, polite, impolite, friendly, foolish, clever 等.例如：
How silly it was of you to give up such a good chance!
你放弃如此好的机会是多么的愚蠢呀!
4. It is up to sb. to do sth. 表示“……应由某人……”.例如：
It's up to you to decide whether to take the job or not.
是否接受这项工作由你来决定.