1:Linda was _____the experiment a month ago, but she changed her mind at the last minute.
选择 B to have started
解析：
1. 本题是个并列句,两个分句分别表达了不同的语气：
--第一分句 Linda was to have started the experiment a month ago 是对过去将来的得虚拟,意思是“琳达本来一个月以前要做实验”,言外之意是并没有按计划进行；
---第二分句 but she changed her mind at the last minute 是真实语气,意思是“但是她在最后的时刻改变了主意”
2. were to（也可以用 was to）表示对将来的虚拟,表示“按计划作某事”；
3. 选项分析
A. was to start 指对现在的将来的虚拟；
B was to have started 指对过去将来的虚拟；
C was to be starting 和 D was to have been starting 在时态表示法上矛盾而且重复,因为 be to do / be to have done 指按计划将要做某事,而趋向动词的进行形式则表示即将发生的将来行为.
2.Would you rather I _____ buying a new bike?
选择 A. decided against
解析：
1. would rather 后的宾语从句要求用虚拟语气,此处是对现在或将来的虚拟,意思是“你非得要我决定反对购买一辆新自行车吗”
2. 选项中只有 A 项的过去形式才符合虚拟要求.其他选项都是真实语气.
3. 如果是对过去的虚拟,必须用“情态动词 + have done” 表示,C 项中没有情态动词,因此不符合要求.
3. He suggested/insisted that they _____ use a trick instead of fighting.
选择 A. should
解析：
1. 原题不完整,主句中缺少谓语动词,根据选项中提供的信息,应该添加要求宾语从句为虚拟语气的动词,如 suggest (建议),insiste（坚持) , demand（要求）, order （命令）等表示主语意愿的动词.
2. 在表示主语意愿动词后的宾语从句要求用 should + 动词原形或者直接用动词原形表示虚拟,选项中只有 A 符合要求.
3. 选择 D 项成了表示强调的 do use,如果不省略 should,出现在其后显然不妥.
4. We would have made a lot of money, but we _____ halfway
选择 A. gave up
解析：
1. 该题与第一题同出一辙.第一分句 would have made 表示对过去的虚拟,即“我们过去本来会赚来很多钱（事实上去不然）”；第二分句是真实语气,指的是“我们却半途而废了”这个真实情况.
2. 根据第一分句所虚拟的过去时间,第二分句当然也是指过去.
5. He was very busy yesterday; otherwise he___A__ to the meeting.
选择 A. would have come
解析：
1. 从 yesterday 可知,后面的“否则他回来参加会议的”指的也应该是过去.意思是昨天本来应该来参加会议,但是由于太忙而没有来.
2. 含有条件的虚拟句,对过去的虚拟应该用 would have done.
3. B. would come 和 C. could come 都是对现在的虚拟,而 D. had come 只能用在条件从句中表示对过去的虚拟.
6. I would have told him the answer had it been possible, but I _____ so busy then.
选择 C. was
解析：
1. but I was so busy then 是真实语气,意思是“当时确实很忙”.
2. A. had been 和 B. were 只能用在条件从句中表示虚拟,但是此处不是.
3. D. would be 是对现在的虚拟.
7 _____ the fog, we should have reached our school.
选择 D. But for
解析：只有表示条件才可能用到虚拟, A. Because of 表示原因,B. In spite of 表示让步,C. In case of 后面必须用动名词,改为 In case of there being the dog（万一有狗）才能用到虚拟, D. But for the dog 表示如果不是那只狗,符合虚拟要求.
8. I can’t stand him. He always talks as though he _____ everything.
选择 A. knew （表示对现在的虚拟）
解析：
从 I can’t stand him 可知,这里说的是“我（现在）忍受不了他”.as though 引导的从句要求用虚拟语气,B. knows 和 C. has known 都表示真实语气,D. had known 是对过去的虚拟.
9 与上一题相似He looked as if he _____ ill for a long time.
选择 D. had been
解析：上题是对现在的虚拟,该题中主句 He looked 表示过去,因此是对过去的虚拟.
10. The two students talked as if they _____ friends for years.
选择 D. had been
解析：道理同上一题,因为句子中的 The two students talked 是过去时态,因此后面虚拟的也是过去.
11. Let’s say you could go there again, how _____ feel?
选择 C. would you
解析：you could go there again（假设你可以再次去那里）是虚设条件,因此 how would you feel 就是在这种虚设条件下可能出现的虚拟感受.