In this task, you need to answer the given multiple-choice question on the gain. Gain is the value by which to multiply the input. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Example Input: Problem: in an election between two candidates , one got 60 % of the total valid votes , 30 % of the votes were invalid . if the total number of votes was 9000 , the number of valid votes that the other candidate got , was : 
Options: a ) 2500 , b ) 2520 , c ) 3000 , d ) 3100 , e ) none of these
Example Output: b

Example Input: Problem: in one hour , a boat goes 8 km along the stream and 2 km against the stream . the sped of the boat in still water ( in km / hr ) is : 
Options: a ) 3 , b ) 5 , c ) 8 , d ) 9 , e ) 10
Example Output: b

Example Input: Problem: one night 17 percent of the female officers on a police force were on duty . if 170 police officers were on duty that night and half of these were female officers , how many female officers were on the police force ? 
Options: a ) 400 , b ) 420 , c ) 450 , d ) 480 , e ) 500
Example Output:
e