What are the top 5 most common elements in the Earth's crust, and what are their percentages? Your response should contain at least 2 placeholders represented by square brackets, such as [source]. The response must have 3 sections. Mark the beginning of each section with SECTION X. Include keywords [silica, aluminum, iron, calcium, sodium]. At the end of your response, please explicitly add a postscript starting with P.S.
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