(7) The maximum value of the function $y=\cos ^{3} x+\sin ^{2} x-\cos x$ is equal to ( ).
(A) $\frac{32}{27}$
(B) $\frac{16}{27}$
(C) $\frac{8}{27}$
(D) $\frac{4}{27}$
$7 \mathrm{~A}$ Hint: The original function can be transformed into $y=\cos ^{3} x-\cos ^{2} x-\cos x+1$. Let $t=$ $\cos x$, then $t \in[-1,1]$. By the derivative method, the maximum point is $x=-\frac{1}{3}$, so the maximum value is $\frac{32}{27}$.