What are the advantages of using cilindro-parabolic collectors over flat panels in solar energy production?

I. They require smaller accumulation tanks.
II. They have lower absorption surfaces.
III. They have lower heat losses.
IV. They are cheaper.
a) I and II are correct.
b) II and III are correct.
c) I, II, and III are correct.
d) II, III, and IV are correct.