Some special square matrices are defined as follows. Nilpotent matrix: A square matrix. A is said to be nilpotent (of order 2)if, `A^(2)=O`. A square matrix is said to be nilpotent of order p, if p is the least positive integer such that `A^(p)=O`.
Idempotent matrix: A square matrix A is said to be idempotent if, `A^(2)=A`.
`e.g.[{:(,1,0),(,0,1):}]` is an idempotent matrix.
Involutory matrix: A square A is said to be involutary if `A^(2)=I`, `I `being the identity matrix.
`e.g..A=[{:(,1,0),(,0,1):}]` is an involutary matrix.
Orthogonal matrix: A square matrix A is said to be an orthogonal matrix if `A' A=I=A A'`
If A and B are two square matrices such that AB=A & BA=B then A&B are

Options

A. idempotent matrices
B. involutary matrices
C. Orthogonal matrices
D. Nilpotent matrices

Answer

A