If for a matrix A, A2 + I = 0, where I is the identity matrix of order 2, then A =
1
\(\left[ {\begin{array}{*{20}{c}} 1&0\\ 0&1 \end{array}} \right]\)
2
\(\left[ {\begin{array}{*{20}{c}} i&0\\ 0&i \end{array}} \right]\)
3
\(\left[ {\begin{array}{*{20}{c}} i&0\\ 0&1 \end{array}} \right]\)
4
\(\left[ {\begin{array}{*{20}{c}} -1&0\\ 0&-1 \end{array}} \right]\)