Task: Question Answering
Input (English): Problem: the radii of two cones are in ratio 2 : 1 , their volumes are equal . find the ratio of their heights . 
Options: ['a ) 1 : 4', 'b ) 1 : 3', 'c ) 1 : 2', 'd ) 1 : 5', 'e ) none of these']
Output (English): a