不带to，变为被动语态时则要带to，此时不定式作主语补足语。在help后，不定式可以带to，也可以不带to。

　　The boss made the workers work 10 hours a day.

　　老板让工人们一天工作10小时。(宾语补足语)

　　The workers were made to work 10 hours a day by the boss.

　　工人们被老板要求一天工作10小时。(主语补足语)

　　　5

　　(江西高考改编)Having finished her project, she was invited by the school to_speak (speak) to the new students.

　　5．不定式作状语

　　动词不定式作状语可表示目的、原因及结果等，其逻辑主语就是句子的主语，因此动词不定式作状语往往用主动式。

　　(1)表示目的：也可用于so as和in order之后表强调。

　　She went to the hospital to see her grandfather yesterday.

　　昨天她去医院看望了她爷爷。

　　She asked me to drive her to the airport in order to catch the 10：00 am plane.

　　为了赶上上午10点的飞机她让我开车把她送到机场。

　　　6

　　①(北京高考改编)To_make (make) it easier to get in touch with us, you'd better keep this card at hand.

　　②(陕西高考改编)To_work (work) out the difficult maths problem, I have consulted Professor Russell several times.

　　③(四川高考改编)-I hope to take the computer course.

　　-Good idea. To_find (find) out more about it, visit this website.

　　④(重庆高考改编)Group activities will be organized after class to_help (help) children develop team spirit.

　　(2)表示结果：可用于enough to, so ... as to, such ... as to, only to ...以及too ... to等结构中。

　　Have you got enough room to seat all of us?

　　你有足够的空间让我们都坐下吗？

　　She is too weak to join us in the outing.

　　她太虚弱以至于不能加入我们的旅行。

　　[点津]　only to do sth.与only doing sth.都可作结果状语，其区别是：only to do sth.表示一个与主语愿望相反或出乎主语意料的结果，或用来暗示最初的未能实现的动作；only doing sth.表谓语动词本身的动作造成的结果，另外，only doing也可作伴随状语表示与谓语动词同时发生的动作。

　　He searched the box only to find nothing.

　　他搜索了这个箱子，没发现什么。

　　His father passed away, only leaving him a little money.

　　他父亲去世了，只给他留下了少量的钱。

　　　7

　　①(天津高考改编)Anxiously, she took the dress out of the package and tried it on, only to_find (find) it didn't fit.

　　②(四川高考改编)Tom took a taxi to the airport, only to_find (find) his plane high up in the sky.

　　(3)表示原因：常用于表情绪或心理活动的形容词之后。

They were surprised to be informed of the news.