1
Stephanie Harvey, "
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" 81.
2
Stephanie Harvey, "
Strategies That Work
," 92-94.
3
Stephanie Harvey, "
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," 82-84.
4
Stephanie Harvey, "
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," 89-90.
5
Stephanie Harvey, "
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," 90-91.
6
World Book, Inc., "
The Digestive System/The Urinary System,
" 5, 8-9.
7
World Book, Inc., "
The Digestive System/The Urinary System,
" 6.
8
World Book, Inc., "
The Digestive System/The Urinary System,
" 6-7.
9
World Book, Inc., "
The Digestive System/The Urinary System,
" 7.
10
World Book, Inc., "
The Digestive System/The Urinary System,
" 7.
11
World Book, Inc., "
The Digestive System/The Urinary System,
" 12-13.
12
World Book, Inc., "
The Digestive System/The Urinary System,
" 14-15.
13
World Book, Inc., "
The Digestive System/The Urinary System,
" 16-17.
14
World Book, Inc., "
The Digestive System/The Urinary System,
" 20-21.
15
World Book, Inc., "
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" 24-25.
16
http://www.nlm.nih.gov/medlineplus/gas.html
17
Norton Greenberger, "
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" 21-22.
18
http://www.treehugger.com/clean-technology/the-flatulence-battle-kangaroos-vs-cattle-and-sheep.html.