Task: Question Answering
Input (English): Problem: a cistern is normally filled in 2 hrs , but takes 2 hrs longer to fill because of a leak on its bottom , if cistern is full , how much time citern would empty ? 
Options: a ) 4 hours , b ) 20 hours , c ) 30 hours , d ) 40 hours , e ) 50 hours
Output (English): a