A4. The domain of the function $f(x)=\frac{3}{2-\cos x}$ is
(A) $[-1,1]$
(B) $\mathbb{R}^{+}$
(C) $\mathbb{R}-\{x ; x=2 k \pi, k \in \mathbb{Z}\}$
(D) $\mathbb{R}$
(E) None of the above.
A4. The domain of the given function is all real numbers, since the equation $2-\cos x=0$ has no solution.