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 of equal lengths take 10 sec and 8 sec respectively to cross a telegraph post . if the length of each train be 120 m , in what time will they cross other travelling in opposite direction ? 
Options: a ) 22 , b ) 12 , c ) 9 , d ) 99 , e ) 21
Example Output: c

Example Input: Problem: a train of 25 carriages , each of 60 meters length , when an engine also of 60 meters length is running at a speed of 60 kmph . in what time will the train cross a bridge 1.0 km long ? 
Options: a ) 2.5 , b ) 3 , c ) 5 , d ) 7 , e ) 9
Example Output: a

Example Input: Problem: the length of the bridge , which a train 160 meters long and travelling at 45 km / hr can cross in 30 seconds , is ? 
Options: a ) 766 m , b ) 156 m , c ) 215 m , d ) 156 m , e ) 156 m
Example Output:
c