Let $C = \begin{bmatrix} 0&B &C \\ -B&0 &D \\ -C&-D&0 \end{bmatrix}$, and $X = \begin{bmatrix} P\\ Q\\ R \end{bmatrix}$, then
$CX$=$\begin{bmatrix} BQ+CR\\ -BP+DR\\ -CP-DQ \end{bmatrix}$
$X^{T}CX=$$\begin{bmatrix} P & Q &R \end{bmatrix}\times \begin{bmatrix}BQ+CR\\-BP+DR\\-CP-DQ \end{bmatrix}$
$\rightarrow \begin{bmatrix} PBQ+PCR-PBQ+QDR-PCR-QDR \end{bmatrix} \rightarrow\begin{bmatrix}PBQ-PBQ+PCR-PCR+QDR-QDR \end{bmatrix}$
$\rightarrow\begin{bmatrix}0\end{bmatrix}$
Option B.