Which of the following is(are) NOT the square of a 3×3 matrix with real entries?

A

$$\begin{bmatrix}1 & 0 & 0\\0 & 1 & 0\\ 0 & 0 & 1\end{bmatrix}$$

B

$$\begin{bmatrix}1 & 0 & 0\\0 & 1 & 0\\ 0 & 0 & -1\end{bmatrix}$$

C

$$\begin{bmatrix}1 & 0 & 0\\0 & -1 & 0\\ 0 & 0 & -1\end{bmatrix}$$

D

$$\begin{bmatrix}-1 & 0 & 0\\0 & -1 & 0\\ 0 & 0 & -1\end{bmatrix}$$