Richard Parsons. (2003). "National Curriculum Science: Earth, Sun and Moon: Unit 5e (National Curriculum Science)". Coordination Group Publications Ltd.
Chicago-viite (17. p.)Richard Parsons. "National Curriculum Science: Earth, Sun and Moon: Unit 5e (National Curriculum Science)". Coordination Group Publications Ltd, 2003.
MLA-viite (9. p.)Richard Parsons. "National Curriculum Science: Earth, Sun and Moon: Unit 5e (National Curriculum Science)". Coordination Group Publications Ltd, 2003.
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