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'.

Example Input: Problem: how long does a train 90 m long traveling at 60 kmph takes to cross a bridge of 170 m in length ? 
Options: a ) sec , b ) sec , c ) sec , d ) sec , e ) sec
Example Output: d

Example Input: Problem: a man swims downstream 76 km and upstream 48 km taking 4 hours each time ; what is the speed of the current ? 
Options: a ) 3 kmph , b ) 1.5 kmph , c ) 3.5 kmph , d ) 6.5 kmph , e ) 7 : 3 kmph
Example Output: c

Example Input: Problem: a can finish a work in 12 days and b can do same work in half the time taken by a . then working together , what part of same work they can finish in a day ? 
Options: a ) 1 / 4 , b ) 1 / 6 , c ) 1 / 7 , d ) 1 / 8 , e ) none of these
Example Output:
a