Here's the key to the exercise on verbs of speculation:
Exercise 1: Here are the five sentences that were incorrect. I've corrected them for you:
1. 1. I can't find my keys. I think I might have left them on my desk at work.
3. Sally's not answering the phone. She might have gone away for the weekend or perhaps she's just gone to the shops.
6. ... or it might not be the right size. Who knows?
7. Jim can't be going out with Sue; she's just got engaged to Doug.
9. It's a shame Mark hasn't come. He must have decided to stay at home.
Exercise 2: possible answers
1. He must have been running/He could have overworked last night
2. He must be on a diet/He's definetely on a diet/He could have eaten too much/He might have already eaten lunch/He might have a stomachache
3.THere must be something going on/There might be a parade today/The subway trains might have stopped working
4. She can't have watered them/There must have been a heat/She could have forgotten to water them/She must have left them in the sun for too long
5. THere might have been a crime/ Some neighbor might have seen something/Someone might have been murdered
6. He must have had a promotion/He might have received good news/It seems he has received good news/He can't have lost his job/ He could have won some money
7. Something must be going on/Something must have happened/ Those people might have seen something
9. you must have forgotten where exactly; this neighborhood is very safe/Your car might have been towed away/ Your car must have been towed away --- this is non parking zone/You might have parked it somewhere else you don't remember/You could have left your car in the parking lot (it is safer there) but you didn't!/You can't have parked your car here (look! it's not even a parking spot!)/They could not have towed your park away
Breaking the ice
3 weeks ago