8. The circle $\rho=D \cos \theta+E \sin \theta$ is tangent to the line of the polar axis if and only if ( ).
(A) $D \cdot E=0$
(B) $D \cdot E \neq 0$
(C) $D=0, E \neq 0$
(D) $D \neq 0, E=0$
8.(C).

From $\rho=D \cos \theta+E \sin \theta$, the rectangular coordinate equation is $\left(x-\frac{D}{2}\right)^{2}+\left(y-\frac{E}{2}\right)^{2}=\frac{1}{4}\left(D^{2}+E^{2}\right)$, or from $\rho=E \sin \theta(E \neq 0)$, it represents a circle tangent to the line of the polar axis.