The diagonals of a rhombus are perpendicular bisectors of each other and they divide the rhombus into four congruent right triangles. If one angle of the rhombus is 60°, then the acute angle of each right triangle is 30°. Let's call the shorter diagonal `d1` and the longer diagonal `d2`. Since `d1` is 8 cm long, then each leg of the right triangle opposite the 30° angle is 4 cm long. Using the properties of a 30-60-90 triangle, we know that the leg opposite the 60° angle is `4 * sqrt(3)` cm long. Since this leg is half of `d2`, then `d2` is `8 * sqrt(3)` cm long.

So, the length of the longer diagonal of the rhombus is **8 * sqrt(3) cm**. This corresponds to answer choice **A**