In this task, you need to answer the given multiple-choice question on geometry. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Example Input: Problem: 80 pie square inches of material of negligible thickness are required to construct a 1 / 16 scale model of a cylindrical barrel . if the diameter of the base of the barrel is 160 inches , then what is the volume of the barrel , to the nearest cubic foot ? 
Options: ['a ) 2 pie', 'b ) 11 pie', 'c ) 178 pie', 'd ) 711 pie', 'e ) 1280 pie']
Example Output: c

Example Input: Problem: the radius of a cylinder is 2 r units and height is 3 r units . find the curved surface ? 
Options: a ) 18 π r 2 , b ) 12 π r 2 , c ) 3 π r 2 , d ) 6 π r 2 , e ) 9 π r 2
Example Output: b

Example Input: Problem: a specialized type of sand consists of 40 % mineral x by volume and 60 % mineral y by volume . if mineral x weighs 1.5 grams per cubic centimeter and mineral y weighs 3 grams per cubic centimeter , how many grams does a cubic meter of specialized sand combination weigh ? ( 1 meter = 100 centimeters ) 
Options: a ) 2 , 400,000 , b ) 2 , 800,000 , c ) 55,000 , d ) 28,000 , e ) 280
Example Output:
a