A5. The maximum value of the function $f(x)=\pi \sin 4 x$ is:
(A) 1
(B) $\pi$
(C) 4
(D) $2 \pi$
(E) $4 \pi$
A5. The maximum value of the function $\sin x$ is 1, so the maximum value of the product $\pi \cdot \sin 4 x$ is $\pi \cdot 1=\pi$.