If $f:\mathbf{R}\to \mathbf{R}, g:\mathbf{R}\to \mathbf{R}$ are continuous functions then the value of the integral

${\int }_{-\pi /2}^{\pi /2} \left[\right(f\left(x\right)+f(-x))$$\left(g\right(x) – g(–x\left)\right)] dx$ is 

• A

  1

• B

  0

• C

  -1

• D

  $\mathrm{\pi }$