Q6

If $f(x)$ is even then
$\int_{-a}^{a}f(x)\,dx=$

A. $2\int_0^a f(a-x)\,dx$

B. $2\int_0^{-a} f(a-x)\,dx$

C. $2\int_a^0 f(x)\,dx$

D. All of the above.