Q: In this task, you need to answer the given multiple-choice question on geometry. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.
Problem: 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 :
Options: ['a ) 1 : 9', 'b ) 1 : 3', 'c ) 3 : 1', 'd ) 1 : 10', 'e ) can not be determined']
A:
a