The state transition matrix ϕ (t) of a system \(\left[ {\begin{array}{*{20}{c}} {{{\dot x}_1}}\\ {{{\dot x}_2}} \end{array}} \right] = \left[ {\begin{array}{*{20}{c}} 0&1\\ 0&0 \end{array}} \right]\left[ {\begin{array}{*{20}{c}} {{x_1}}\\ {{x_2}} \end{array}} \right]\)is

• A. \(\left[ {\begin{array}{*{20}{c}} t&1\\ 1&0 \end{array}} \right]\)
• B. \(\left[ {\begin{array}{*{20}{c}} 1&0\\ t&1 \end{array}} \right]\)
• C. \(\left[ {\begin{array}{*{20}{c}} 0&1\\ 1&t \end{array}} \right]\)
• D. \(\left[ {\begin{array}{*{20}{c}} 1&t\\ 0&1 \end{array}} \right]\)