Which of the following is true concerning continental crust?

Continental crust contains radioactive elements such as uranium, thorium, and potassium, so choice a is false. It is generally less dense than the mantle, not made mostly of heavier, denser minerals, so choice b is false. Heat moves through the crust mainly by conduction, which is less efficient than the mantle’s convection, so choice c is false. Therefore, “None of the above” is correct.

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