A linear constant parameter continuous-time system has the following A matrix in its state representation \[\mathop {\rm{X}}\limits^ \cdot = {\rm{AX}} + {\rm{Bu}}{\rm{.}}\]
\[{\rm{A}} = \left[ {\begin{array}{*{20}{c}} 0&\alpha \\ \alpha &0 \end{array}} \right]\]
Which one of the following is the natural response of the system following the application of any input?