A solar furnace is to be built so that incoming parallel sunlight is brought to a focus 0.50 m in front of the reflecting surface. Which of the following choices of mirror type and radius of curvature will satisfy this requirement?
a) Concave mirror, radius of curvature 0.50m
b) Convex mirror, radius of curvature 1.0m
c) Concave mirror, radius of curvature 1.0m
d) Concave mirror, radius of curvature 0.25m