必做题目：
1.Sometimes I wish I am living in a different time and a different place.
2.Had electronic computers not been invented,many problems on space flight could not be solved.
选做题目：
★It is obligatory that every young man serves in the armed forces.
必做答案：
1.应该将am living改为were living.该题考察wish+that从句的虚拟表达法。Sometimes是一个频率副词，表示现实里经常性的动作，显然这里需要的动词虚拟式为过去时形式。
2.应该将could not be改为could not have been。该题考察非真实条件句虚拟语气的用法。根据从句可知此处是与过去事实相反的虚拟，且solve与many problems之间为被动关系，因而要用could not have been solved的表达形式。
选做答案：应该将serves改为serve。该题考察obligatory之类的形容词引导主语从句，从句中要使用虚拟语气，从句中动词形式为should+动词原形，should可以省略。
