The given expression is 8a^3 - 27. This expression represents the difference of two cubes. The formula for the difference of two cubes is a^3 - b^3 = (a - b)(a^2 + ab + b^2). In this case, a is 2a and b is 3. Plugging these values into the formula, we get (2a - 3)(4a^2 + 6a + 9). Therefore, the correct answer is 8a^3 - 27.