Circle the answer that correctly completes each sentence.

1. The Incas didn’t have any sophisticated machines or work animals. The temples ( must / couldn’t / may ) have been built exclusively by human hands.

2. Dinosaurs may not have died off gradually as the result of climate change. They ( had to / could / would ) have been killed off quickly by some sudden event.

3. I don’t believe in any of those other crazy theories. Stonehenge ( might have been / were / had to have been ) built by ancient Britons many years ago.

4. The Nazca lines are incredible, but I’m certain they weren’t created by people who lived 1,500 years ago. The ancient people ( couldn’t have / would have / must have ) had the knowledge to create something so accurate.

5. Conspiracy fans continue to consider the story of Roswell aliens. They believe that UFOs ( might / couldn’t / had to ) have crashed in the desert.

6. The Mary Celeste ( might have been / had to have been / had been ) attacked by pirates. No one knows for sure.

7. It’s obvious that something terrible happened. The crew ( had to have / would have / might ) abandoned the ship during the incident. There’s no other explanation.

*On a separate sheet of paper, rewrite the sentenoes with perfect modals in the active voice.
1. Scientists believe that (it's possible some form of life existed) on the planet Mars billions of years ago
Ex: Scientists believe that some form of life could have existed on the planet Mars billions of years ago
2. Heyerdahl thought (it was possible that they had come) on a raft like the Kon-Tiki.
.............................................................................................................
3. Some historians think that (the Rapa Nui islanders probably didn't move) the moai using logs.
.............................................................................................................
4. (It's possible someone forced the pilot) to fly the plane to a different location.
.............................................................................................................
5. Experts suggest that originally (the Ropa Nul people most likely wrote) on banana leaves
.............................................................................................................
6. (There's no question that hunting was) the cause of the carrier pigeon's extinction as a species.
.............................................................................................................

*On a separate sheet of paper, rewrite the sentenoes with perfect modals in the active voice.
1. Scientists believe that (it's possible some form of life existed) on the planet Mars billions of years ago
Ex: Scientists believe that some form of life could have existed on the planet Mars billions of years ago
2. Heyerdahl thought (it was possible that they had come) on a raft like the Kon-Tiki.
.............................................................................................................
3. Some historians think that (the Rapa Nui islanders probably didn't move) the moai using logs.
.............................................................................................................
4. (It's possible someone forced the pilot) to fly the plane to a different location.
.............................................................................................................
5. Experts suggest that originally (the Ropa Nul people most likely wrote) on banana leaves
.............................................................................................................
6. (There's no question that hunting was) the cause of the carrier pigeon's extinction as a species.
.............................................................................................................

*On a separate sheet of paper, rewrite the sentenoes with perfect modals in the active voice.
1. Scientists believe that (it's possible some form of life existed) on the planet Mars billions of years ago
Ex: Scientists believe that some form of life could have existed on the planet Mars billions of years ago
2. Heyerdahl thought (it was possible that they had come) on a raft like the Kon-Tiki.
.............................................................................................................
3. Some historians think that (the Rapa Nui islanders probably didn't move) the moai using logs.
.............................................................................................................
4. (It's possible someone forced the pilot) to fly the plane to a different location.
.............................................................................................................
5. Experts suggest that originally (the Ropa Nul people most likely wrote) on banana leaves
.............................................................................................................
6. (There's no question that hunting was) the cause of the carrier pigeon's extinction as a species.
.............................................................................................................

Complete the sentences using the words in parentheses.

14. Animals.............(should / train) with a combination of firmness and affection.

15. Dogs are usually used to help people with disabilities but I have heard that other animals................ (can / use) as well.

16. Gina’s dog.................(might / not / find) because it wasn’t wearing its dog tag with Gina’s

phone number on it.

17. With all the new technology that is available in medical science, why do animals still........... (have to / use) for research?

18. I don’t believe that any animal............(should / keep) in a cage. That’s why I hate zoos.

19. The illegal hunting of wildlife.............(must / prevent) or else some important species will disappear.

20. Sang’s dog............. (could / be) better trained. It never obeys her.

21. A lot more............(could / do) to improve conservation efforts for chimpanzees.