此外，这种不定式结构还可作主语，表语，和介词宾语等。
　　How to live a happy life is a difficult question to answer. 怎样过幸福生活是个很难回答的问题
　　The question is whom to choose for the position. 问题是这个位置选谁。
　　That was a discussion about how to increase their strength. 那是一次关于怎样增强他们力量的讨论。
　　He said nothing about what to do with her. 关于拿她怎么办，他啥也没说。
　　She asked my suggestion just now about where to go for her holidays. 关于去哪里度假，她刚才征求了我的意见。
　　3、有些动词需要不定式作宾语补足语。这种动词常见的有：ask请求，advise劝告，allow允许，beg乞求，believe相信，call on号召，cause促使，compel强迫，command指挥，direct指导，enable使…能够，encourage鼓励，expect期望，feel觉得，force迫使，get使得，hate不喜欢，have使，hear听见，help帮助，inspire鼓舞，intend 打算,invite邀请,instruct指示，know知道，lead引导，let让，like喜欢，listen to 听，look at看，make 使得, notice注意到, observe观察，order命令，permit允许，persuade说服，prefer更喜欢，press施加压力，remind提醒，request请求，teach教，tell告诉，urge敦促，want 想要，warn警告，wish希望，等等。
　　I asked my mother to buy a new bike for me. 我请求妈妈给我买辆新自行车。
　　Tony knew his girl friend to be a shy college student. 托尼知道他的女朋友是一个害羞的大学生。
　　They helped you to get on the bus, didn’t they? 他们帮你上了汽车， 是吗?
　　4、有些动词要求省掉to的不定式作宾语补语。这样的动词有：feel觉得，have使，hear听见，help帮助，let让，listen to 听，look at看，make使，notice 注意，see看见，observe 观察，watch观看 等，一类是感官动词，一类是使役动词。
　　A policeman saw the accident happen. 一位警察看见事故发生。
　　We listened to her talk about her experience abroad. 我们听她讲国外的经历。
　　We’d be glad to have you work with us. 我们会很高兴有你和我们一起工作。
　　上述help后面的不定式省掉to与保留to都可以。在被动语态中，上述动词后面的不定式要把省去的to还原。
　　I heard the dog come in. 我听见那条狗进来。
　　=The dog was heard to come in. 有人听见那条狗进来。
　　I saw her go out by bike. 我看见她骑着自行车出去了。
　　=She was seen to go out by bike. 有人看见她骑着自行车出去了。
　　Can I help (to) lift this heavy box?   我可以帮着搬起这个沉重的箱子吗?
　　You may as well help me (to)get things straight. 你不妨帮我把东西整理好。
　　She helped the old woman (to) cross the street. 他帮助那位老妇人过街
　　在had better(最好)，would rather(宁愿)，would sooner(宁愿)，would (just) as soon(宁愿)，cannot but(不能不，不由得不)，cannot help but(不能不，不由得不)等成语后面也跟不带to的不定式：
　　He would rather listen to others than talk himself. 他宁愿听别人也不愿自己说。
　　He would sooner play than work. 他宁愿玩也不愿干活。
　　You had better go away right now. 你最好立即就走。
　　I would rather take this method. 我倒愿意采取这个办法。
　　I’d rather walk than take a bus. 我宁可走也不愿坐公共汽车。
　　She’d rather die than lose the children. 她宁可死也不愿失去孩子们。
　　I’d rather not have eggs and bacon for breakfast.
　　She’d sooner stay at home.
　　I would as soon do it by myself.
　　I would just as soon stay as go. 我宁愿住下也不愿去。