C级： 1
1．Pigeons and People 1
2．Around and Around 4
3．Birds of Prey 7
4．Fine Feathers 10
5．The Air Around You 13
6．Ice From a Summer Sky 16
7．Strong Girls 19
8．Clean Sweep 22
9．Tilt and Turn 25
10．Fireworks 28
11．Desert King 31
12．The Great Wall 34
13．Earthquakes 37
14．Stories Without Words 40
15．At Work in the Sky 43
16．Rainmakers 46
17．They Have to Be Fast 49
18．A Heap or a Handful 52
19．What Time Is It？ 55
20．Around the World with a Hobby 58
D级 63
1．The First Americans 63
2．A Plant Surprise 66
3．Using Machines 69
4．Indian Houses 73
5．One of Nature s Wonders 77
6．The Ship of the Desert 80
7．About the Lapps 83
8．Some Queer Plants 86
9．More About Desert Nomads 89
10．A Big Change in Travel 92
11．Seeds with Umbrellas 95
12．Houses of the Desert Nomads 98
13．Life in Lapland 101
14．More About Desert People 104
15．Three Man-Made Wonders 107
16．Would You Like Pioneer Life？ 110
17．How Desert People Dress 114
18．The Story of Light 117
19．Learning by Doing 120
20．Moving to the West 124