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1
Solar System (nine planets)
03:49
$0.15
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2
Continents
03:56
$0.15
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3
Waters (the oceans)
04:24
$0.15
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4
50 States and Capitols (USA)
09:22
$0.15
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5
Time (units of time)
02:26
$0.15
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6
The Body (human body systems)
02:28
$0.15
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7
Matter (states of matter)
02:52
$0.15
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8
Scientific Method
02:22
$0.15