For k>0 let R be the region bounded by the x-axis and the graph of y=ksinx for 0≤x≤π. A solid has base R and cross sections perpendicular to the x-axis that are semicircles whose diameters lie in R. If the volume of the solid is π, what is the value of k?
a) π2
b) π4
c) π22
d) π4