1．(2018·全国卷Ⅰ)You don't have to run fast or for long________ (see) the benefit.
解析：to see 此处意为：你不必跑很快或很久就能看到它的好处。分析句子结构可知，此处应该使用不定式形式作目的状语。
2．(2018·全国卷Ⅱ)The government encourages farmers to grow corn instead of rice ______ (improve) water quality.
解析：to improve 根据“改善水质”是“政府鼓励农民种植玉米而不种植水稻”的目的，可知此处应用动词不定式作目的状语。
3．(2018·全国卷Ⅲ)Once his message was delivered, he allowed me ________ (stay) and watch.
解析：to stay allow sb.to do sth.为固定搭配，意为“允许某人做某事”。
4．(2018·6月浙江高考)While regularly eating out seems to ________ (become) common for many young people in recent years, it's not without a cost.
解析：have become 根据后面的时间状语in recent years可知，此处应该用动词不定式的完成时。
5．(2017·全国卷Ⅰ)They are required ________ (process) the food that we eat, to recover from injury and for several other bodily functions.
解析：to process require sb.to do sth.为固定搭配，意为“需要某人做某事”。
6．(2016·四川高考)For 25 days, she never left her baby, not even to find something ________ (eat)!
解析：to eat 句意：25天中，她寸步不离她的孩子，甚至不去找东西吃！不定式to eat作定语，修饰前面的不定代词something。
