List of top Data Sufficiency and Logical Reasoning Questions on Data Sufficiency - Mensuration

If \(C_1\) and \(C_2\) are the circumferences of the outer and inner circles respectively, what is \(C_1 : C_2\)?
(I) The two circles are concentric.
(II) The area of the ring is \(\frac{2}{3}\) the area of greater circle.