Which of the following is an orthogonal matrix ?
A. `[(6//7,2//7,-3//7),(2//7,3//7,6//7),(3//7,-6//7,2//7)]`
B. `[(6//7,2//7,3//7),(2//7,-3//7,6//7),(3//7,6//7,-2//7)]`
C. `[(-6//7,-2//7,-3//7),(2//7,3//7,6//7),(-3//7,6//7,2//7)]`
D. `[(6//7,-2//7,3//7),(2//7,2//7,-3//7),(-6//7,2//7,3//7)]`