The tangent to the curve y=1−x2 at x=α , where 0<α<1 , meets the axes at P and Q . If α varies and the minimum value of the area of the ΔOPQ is k times the area bounded by the axis and the part of the curve for 0<x<1 , then k is equal to
a. 2/3
b. 75/16
c. 25/18
d. 2/3