Which expression is a difference of cubes?

A difference of cubes has the form x³ − y³, so both terms must be perfect cubes. In choice D, 64 = 4³, c¹⁵ = (c⁵)³, and d²⁷ = (d⁹)³. Thus 64c¹⁵ − d²⁷ is a difference of cubes.

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