If α and β are the real roots of x2+px+q=0 and α4,β4 are the roots of x2−rx+s=0. Then the equation x2−4qx+2q2−r=0 has always (α=β,p=0,p,q,r,s∈R):
(a) one positive and one negative root
(b) two positive roots
(c) two negative roots
(d) can't say anything