① To complete the 30 storied building in one year was quite a difficult task.
② To do that implies taking responsibility.
① It is important for modern young people to master at least two foreign languages.
a) It is+形容词(easy, important, difficult, foolish, inconvenient, unnecessary, right, wrong...)+( for/of sb.)+不定式. 例如：
① It is essential to reserve a table in advance of Christmas Eve.
② It is hard to put my hopessintoswords.
③ It is not easy to catch fish with your hands only.
④ It is important for us young people to learn English and master it.
b) It is+名词(a pleasure, a pity, a pleasant thing, one’s duty, an honor, a shame, a crime, no easy job...)+不定式. 例如：
① It is a sheer waste of time to read that kind of trash.
② It is a pity to have to go without her.
③ It is a glorious death to die for the people.
c) It takes (sb.) some time (hours, months, days, a lot of time, patience...)+不定式.例如：
① It takes me three hours to learn English each day.
② It took them half the night to get home in the snow.
2. 动词不定式作表语不定式作表语常表示将来的动作，主语常常是表示意向、打算、计划的词，如wish, idea, task, purpose, duty, job等。例如：
① The most important thing for one’s health is to have plenty of exercise.
② My chief purpose has been to point out the difficulties of the matter.
③ The purpose of the organization is to greet all new comers to the city and to provide them with any necessary information.
④ What I wanted was to get the work done as quickly as possible.
afford, agree, apply, arrange, ask, attempt, beg, begin, care, choose, claim, consent, demand, decide, desire, determine, expect, fail, hope, hesitate, hate, intend, learn, like, manage, mean, neglect, offer, plan, prepare pretend, promise, refuse, resolve, seek, tend, threaten, want等。例如：
① I like to go out for walks in the warm sunshine in spring.
② My mother hates to move from place to place, for she feels tired.I decide to work hard and get doctor’s degree.
③ The room is designed to be my study, but now it has to be used as a bedroom for the children.
④ She failed to finish the assignment in time, and she was worried about it.
① We found it impossible to get everything ready in time. I think it important to learn English well in college. 使用这种句型的常见动词有：believe, consider, declare, feel, find, guess, imagine, prove, realize, suppose, think,等。