Let $A = \left[ \begin{array} { c c c } 5 & 5 \alpha & \alpha \\ 0 & \alpha & 5 \alpha \\ 0 & 0 & 5 \end{array} \right]$. If $\left| A ^ { 2 } \right| = 25$, then $| \alpha |$ equals\\ (1) $5 ^ { 2 }$\\ (2) 1\\ (3) $1 / 5$\\ (4) 5