  We prove a special case of the Dynamical Andre-Oort Conjecture formulated by
Baker and DeMarco. For any integer d>1, we show that for a rational plane curve
C parametrized by (t, h(t)) for some non-constant polynomial h with complex
coefficients, if there exist infinitely many points (a,b) on the curve C such
that both z^d+a and z^d+b are postcritically finite maps, then h(z)=uz for a
(d-1)-st root of unity u. As a by-product of our proof, we show that the
Mandelbrot set is not the filled Julia set of any polynomial with complex
coefficients.
