Factor completely. \[ a^{3}-27 \] Select the correct choice below and, if necessary,

Step 1 ：Given expression is \(a^3 - 27\)

Step 2 ：This is a difference of cubes, which can be factored using the formula \(a^3 - b^3 = (a - b)(a^2 + ab + b^2)\)

Step 3 ：In this case, \(a = a\) and \(b = 3\)

Step 4 ：Applying the formula, we get \(a^3 - 27 = a^3 - 3^3 = (a - 3)(a^2 + 3a + 9)\)

Step 5 ：So, the completely factored form of \(a^3 - 27\) is \(\boxed{(a - 3)(a^2 + 3a + 9)}\)