\text { Let } n \in \mathbb{Z} \text { . Show }\left\{\begin{array}{ll} n^{3} \equiv 0(\bmod 4) & \text { if } n \text { is even } \\ n^{3} \equiv

1(\bmod 4) & \text { if } n \equiv 1(\bmod 4) \\ n^{3} \equiv 3(\bmod 4) & \text { if } n \equiv 3(\bmod 4) \end{array}\right.