| Unit 1 | 4 | How did the Olympic Games begin? | 
		
			| Unit 2 | 6 | How do crocodiles clean their teeth? | 
		
			| Unit 3 | 8 | What is the Statue of Liberty? | 
		
			| Unit 4 | 10 | Why do leaves change color in the fall? | 
		
			| Unit 5 | 12 | Where did the ideas for our government come from? | 
		
			| Unit 6 | 14 | Why does a jumping bean jump? | 
		
			| Unit 7 | 16 | What is Earth Day? | 
		
			| Unit 8 | 18 | What is a mongoose? | 
		
			| Unit 9 | 20 | How do people know what time it is? | 
		
			| Unit 10 | 22 | What is the praying mantis? | 
		
			| Unit 11 | 24 | Who was Anne Frank? | 
		
			| Unit 12 | 26 | How is paper made? | 
		
			| Unit 13 | 28 | What was the Titanic? | 
		
			| Unit 14 | 30 | What is the powder on a butterfly’s wings? | 
		
			| Unit 15 | 32 | Why is Mt. Rushmore famous? | 
		
			| Unit 16 | 34 | What plant eats meat? | 
		
			| Unit 17 | 36 | What was a victory garden? | 
		
			| Unit 18 | 38 | Where does chocolate come from? | 
		
			| Unit 19 | 40 | What tea party became a part of history? | 
		
			| Unit 20 | 42 | Where does the trap-door spider live? | 
		
			| Unit 21 | 44 | What is recycling? | 
		
			| Unit 22 | 46 | What is a shooting star? | 
		
			| Unit 23 | 48 | Where was the first subway started? | 
		
			| Unit 24 | 50 | Why is the lionfish left alone? | 
		
			| Unit 25 | 52 | How has the potato changed history? | 
		
			| Unit 26 | 54 | How do dolphins sleep without drowning? | 
		
			| Unit 27 | 56 | What is the birthday of the United States of America? | 
		
			| Unit 28 | 58 | How does gravity affect the tides? | 
		
			| Unit 29 | 60 | Where do people pray to mountains? | 
		
			| Unit 30 | 62 | What bugs us every 17 years? | 
		
			| Unit 31 | 64 | What can be learned from ancient graves? | 
		
			| Unit 32 | 66 | Why did the dinosaurs die out? | 
		
			| Unit 33 | 68 | What colorful art form began in America? | 
		
			| Unit 34 | 70 | What happens underground during winter? | 
		
			| Unit 35 | 72 | How did Maggie and Lillian Rogers learn so much about the White House? | 
		
			| Unit 36 | 74 | Why don’t people ride zebras? | 
		
			| Unit 37 | 76 | Who holds the record for staying alive at sea the longest? | 
		
			| Unit 38 | 78 | Why do you look upside down in a spoon? | 
		
			| Unit 39 | 80 | What is Carnegie Hall? | 
		
			| Unit 40 | 82 | What is ball lightning? | 
		
			| Unit 41 | 84 | Who was Calbraith Rodgers? | 
		
			| Unit 42 | 86 | Where did the first magnets come from? | 
		
			| Unit 43 | 88 | Why did the Spanish come to the Americas? | 
		
			| Unit 44 | 90 | What animal makes bubbles on leaves? | 
		
			| Unit 45 | 92 | What was so special about climbing Half Dome? | 
		
			| Unit 46 | 94 | What unique thing do bowerbirds do? |