all tenses in one exercise - from Bywater's A Proficiency Course in English

2. After he had eaten an enormous dinner, he fell asleep and was dreaming peacefully when a lump of coal fell on to the hearth and woke him up. - Could you please tell me, why there is past perfect used? Is it necessary here? Could I use simple past? -- Your're right, it's not strictly necessary because the other words give the sequence by using "after." But the past perfect is used to refer to a time in the past that was even more in the past than another past event. Here, the "eating" was earlier than the "falling."

3. I had been living / lived in that flat for several years before I decided / had decided to look round for something more central. - Wchich version is correct? Could I simply use the simple past tense here? We have words like "before" don't we? So is present perfect necessary (especially in the second part) ? -- This one is beyong me to explain at the moment. If no one else comes by to attack it, I'll return to it.

4. I shall / will have finished the book in about twenty minutes' time; can;t you wait until then? - The key gives "shall" and I don't know whether "will" and "shall" differ in any way... do they? Besides, I wanna know whether I could simply say "I will finish the book in about 20 minutes..." and if not, why??? -- Please don't use "wanna." In practical terms, "I shall" is simply not used in American English. To express simple future for the first person, "shall" is technically correct (while "will" is more of a statement of dermination or obligation). By the time it is 20 minutes from now, I shall have finished the book. If you are thinking about it from the point of view of that future, then use "have finished." If you are simply talking about projecting your estimate abour the future using right now as the base, use simply shall/will.

Say I'm driving someplace, and someone asks when we'll get there: "I will arrive in about 20 minutes, I think." But if someone says that I look tired, I can say "By the time I arrive (projecting into the future) I will have been driving for ten hours today."

5. The Incas were beaten in battle by the Spanish conquistadores and, after being held / were held / they had been held in captivity for some time, their Emperor was murdered. - The key says "had been held" and I have no idea why... couldn't I simply say "were held" ? or "being held" ? why not? -- I certainly think you can say "being held" or "they were held." I don't know why the book lists only "they had been held." Again, the "after" provides the sequence for you, so the past perfect isn't necessary.

6. Have you seen my glasses? - Can I say "Did you see my glasses" ? why/why not? -- The "have you" seems more recent.

7. When I arrived on the field yesterday, preparations were / had been in the full swing for the Fair which opens today... - again, sp vs p. perf. - The key says "were" and I would say "had been" ... is it wrong to use the past perfect here? what would it take to use it? adding a word like "already" maybe? -- Yes, you would need to say something like "had been in full swing for several hours."

8. I met your sister yesterday and I think / thought she was looking very well / she looks very well. - Can I use simple present? If I mean that she looks fine, like...  kind of... generally! And does "thought" imply that I thought that in the past and I don't think that anymore? or does it mean more like "generally" ? Could I use "I think..." here? why not? -- Eh, it sounds funny to talk in the present about an event that happened yesterday.

9. Tolstoy tried / had been trying / had tried to educate his serfs but after he had been working / working / having been working at it for 20 years he got discouraged and gave it up. - Here, I'm completely confused... The key says "tried" and "had been working" ... dunno why... and why the rest is wrong... -- Again, I'm not up for this one right now. If no one else comes along, I'll try again.