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

Ex Input:
Problem: convert 500 miles to km ?
Options: a ) 600 km , b ) 700 km , c ) 800 km , d ) 900 km , e ) 1000 km

Ex Output:
c

Ex Input:
Problem: what percent of a day is 7 hours ?
Options: a ) 29.2 % , b ) 12.5 % , c ) 13 % , d ) 11.3 % , e ) none of these

Ex Output:
a

Ex Input:
Problem: a train covers a distance of 12 km in 10 minutes . if it takes 7 seconds to pass a telegraph post , then the length of the train is
Options: a ) 100 m , b ) 120 m , c ) 140 m , d ) 160 m , e ) 170 cm

Ex Output:
c