3. In the $x y$-plane, which of the following is the reflection of the graph of
$$
y=\frac{1+x}{1+x^{2}}
$$
about the line $y=2 x$ ?
(A) $x=\frac{1+y}{1+y^{2}}$;
(B) $x=\frac{-1+y}{1+y^{2}}$;
(C) $x=-\frac{1+y}{1+y^{2}}$
(D) $x=\frac{1-y}{1+y^{2}}$;
(E) None of the above.
3. Answer: (E).
(A) and (B) are the reflections with respect to $y=x$ and $y=-x$ respectively; (C) and (D) are the rotations about the origin by $90^{\circ}$ and $-90^{\circ}$ respectively.