Task: Question Answering
Input (English): Problem: one night 20 percent of the female officers on a police force were on duty . if 100 officers were on duty that night and half of these were female officers , how many female officers were on the police force ? 
Options: a ) 90 , b ) 180 , c ) 250 , d ) 500 , e ) 1,000
Output (English): c