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: two trains 140 m and 160 m long run at the speed of 60 kmph and 40 kmph in opposite directions in parallel tracks . the time which they take to cross each other is ? 
Options: a ) 5.6 sec , b ) 8.9 sec , c ) 10.8 sec , d ) 12.6 sec , e ) 15 sec
Example Output: c

Example Input: Problem: in what time will a train 100 metres long cross an electric pole , if its speed be 144 km / hr ? 
Options: a ) 2.5 sec , b ) 4.25 sec , c ) 5 sec , d ) 12.5 sec , e ) none
Example Output: a

Example Input: Problem: a tank is filled by 3 pipes with uniform flow . the first two pipes operating simultaneously fill the tan in the same time during which the tank is filled by the third pipe alone . the 2 nd pipe fills the tank 5 hours faster than first pipe and 4 hours slower than third pipe . the time required by first pipe is 
Options: a ) 13 hours , b ) 45 hours , c ) 15 hours , d ) 12 hours , e ) 11 hours
Example Output:
c