1. jack wishes that he _____ business instead of history when he was in university.
a. studied
b. had been studying
c. study
d. had studied
2. the millions of calculation involved, had they been done by hand, _____ all practical value by the time they were finished.
a. had lost
b. would lose
c. would have lost
d. should have lost
3. it is essential that these application forms _____ back as early as possible.
a. must be sent
b. are sent
c. will be sent
d. be sent
答案：
1. d
译文：杰克宁愿在大学学的是商务而不是历史。
本句是wish 后接虚拟语气的用法。在wish 后面所接的宾语从句中，要用虚拟语气结构。
其主要形式有三种：
表示对现在情况的虚拟：wish 主语 动词过去式；
表示对过去情况的虚拟：wish 主语 had 过去分词；
表示对将来情况的虚拟：wish 主语 would 动词原形。
2. c
译文：数以百万计的相关计算，如果由人工操作的话，到计算完成时早已失去其实用价值。
本句是条件句中与过去事实相反的虚拟语气结构的用法。由省略if 的从句(had they been done by hand)中的时态可知，c为正确答案。
3. d
译文：这些申请表尽快寄出是极其必要的。
本句涉及主语从句中的虚拟语气用法。在it is important/necessary/… that-clause 结构中，that 从句中谓语动词常用虚拟语气，其形式为：(should) 动词原形。这一结构是否用虚拟语气取决于主句it is important/… that 中的形容词(如本句中的important )。