Task: Question Answering
Input (English): 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']
Output (English): a