The radius of base of solid cone is 9 cm and its height is 21 cm. It cut into 3 parts by two cuts, which are parallel to its base. The cuts are at height of 7 cm and 14 cm from the base respectively. What is the ratio of curved surface areas of top, middle and bottom parts respectively?

A

1 : 4 : 8

B

1 : 3 : 5

C

1 : 3 : 9

D

1 : 6 : 12