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: if 20 typists can type 50 letters in 30 minutes , then how many letters will 40 typists working at the same rate complete in 1 hour ? 
Options: a ) 400 , b ) 500 , c ) 350 , d ) 250 , e ) 200

Ex Output:
a


Ex Input:
Problem: the speed of a boat in still water is 15 km / hr and the rate of current is 3 km / hr . the distance travelled downstream in 12 minutes is 
Options: a ) 1.2 km , b ) 1.8 km , c ) 2.4 km , d ) 3.6 km , e ) 1.6 km

Ex Output:
d


Ex Input:
Problem: a train is running at a speed of 40 km / hr and it crosses a post in 19.8 seconds . what is the length of the train ? 
Options: a ) 190 metres , b ) 160 metres , c ) 200 metres , d ) 220 metres , e ) 250 metres

Ex Output:

d