In a trapezium ABCD, AB is parallel to DC, AB = 3*DC, and the diagonals of the trapezium intersect at O. The ratio of the area of ∆OCD to the area of ∆OAB is:	Choose the correct choice from the following choices:
A) 1 : 9
B) 1 : 3
C) 3 : 1
D) 1 : 10
E) can not be determined

Rationale: triangles are similar , so ratio will be 1 : 9 a
Answer: A