Exercise 33
1. cars 2. gas 3. pessimists 4. air 5. optimists 6. colors

Exercise 34
1. held 2. games 3. winners 4. sports 5. wars 6. rules

Exercise 35
1. louder 2. women 3. voices 4. men 5. reason 6. scientists

Exercise 36
1. preserve 2. wild 3. ago 4. spend 5. animals 6. country

Exercise 37
1. earth 2. lived 3. dinosaurs 4. changed 5. fossils 6. animals

Exercise 38
1. gestures 2. means 3. show 4. phrase 5. Chinese 6. English

Exercise 39
1. environment 2. humans 3. provide 4. trees 5. animals 6. fire

Exercise 40
1. speak 2. first 3. language 4. learns 5. mother 6. local

Exercise 41
1. school 2. work 3. o'clock. 4. bus 5. day 6. weekend

Exercise 42
1. live 2. big 3. aunts 4. sister 5. emails

Exercise 43
1. records 2. book 3. breaking 4. impossible 5. world

Exercise 44
1. birthday 2. babies 3. common 4. national 5. doctors

Exercise 45
1. museum 2. frogs 3. scientists 4. find 5. male

Exercise 46
1. machines 2. people 3. statues 4. ancient 5. built

Exercise 47
1. policemen 2. city 3. thieves 4. paid 5. horses

Exercise 48
1. city 2. streets 3. artists 4. festival 5. performances

Exercise 49
1. burglaries 2. people 3. houses 4. police 5. happen

Exercise 50
1. wool 2. sheep 3. sweaters 4. socks 5. customers

Exercise 51
1. birds 2. plane 3. weather 4. flew 5. way

Exercise 52
1. school 2. jam 3. making 4. friends 5. business