请看下面一道题：The chemistry teacher required the students _________ more attention _________ the lab clean.
A. to pay, to keep              B. to paying, to keeping
C. to pay, to keeping           D. paying, keeping

【分析】此题容易误选A，认为空白处应填两个不定式。其实正确答案是C，第一空填不定式，即套用 require sb to do sth (要求某人做某事)句型，而第二空则应填 to keeping，因为 pay attention to(注意)中的to to 也是介词，不是不定式符号，后接动词时应用动名词，而不是动词原形： devote one’s time to doing sth 把某人的时间用于(奉献于)做某事be [get] used to doing sth习惯于做某事be [get] used to doing sthbe equal to doing sth 等于做某事，能胜任做某事What do you say to doing sth 你认为做某事怎么样be accustomed to doing sth 习惯于做某事look forward to doing sth 盼望做某事be opposed to doing sth 反对做某事object to doing sth反对做某事stick to doing sth 坚持做某事get down to doing sth 开始做某事take to doing sth 喜欢上做某事admit to doing 承认做了某事pay attention to doing sth 注意做某事