Task: Question Answering
Input (English): Problem: if a : b = 3 : 4 , b : c = 7 : 9 , c : d = 5 : 7 , find a : d ? 
Options: a ) 5 / 12 , b ) 5 / 15 , c ) 5 / 10 , d ) 5 / 11 , e ) 5 / 13
Output (English): a