2）Although NewJersey is called the "Garden State",over three-quarters of its area is used for non-agricultural purposes,which leaves only a small portion of land available for cultivation. 这是princeton中的一道摸考题的答案，用which来指代整个句子，我们应该彻底屏弃是吧？
3）Three out of seven people will file((a tax returns with a disk found in software stores and accounting texts)). why a tax returns with a disk?为什么用a tax returns with a disk？就像OG中three out of every four ..... also own a bicycle.....那道一样。不过我还是不太清楚此题为什么要用single形式？是因为要表达都是同一种税表的原因吗？
4)lead to此处的to是介词吧？
5）关于动词不定式的完成时态的用法，大家能给出定论了吗？ 就是 do+ to have done的这种结构。