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: pipe a fills a tank of capacity 850 liters at the rate of 40 liters a minute . another pipe b fills the same tank at the rate of 30 liters a minute . a pipe at the bottom of the tank drains the tank at the rate of 20 liters a minute . if pipe a is kept open for a minute and then closed and pipe b is open for a minute and then closed and then pipe c is open for a minute and then closed and the cycle is repeated , when will the tank be full ? 
Options: a ) 42 minutes , b ) 51 minutes , c ) 39 minutes , d ) 40 minutes 20 seconds , e ) none of these

Ex Output:
b


Ex Input:
Problem: the length of the bridge , which a train 140 metres long and travelling at 45 km / hr can cross in 30 seconds , is ? 
Options: a ) 255 , b ) 267 , c ) 235 , d ) 277 , e ) 211

Ex Output:
c


Ex Input:
Problem: a tank can be filled by a tap in 20 minutes and by another tap in 60 minutes . both the taps are kept open for 10 minutes and then the first tap is shut off . after this , the tank will be completely filled in what time ? 
Options: a ) 10 mins , b ) 15 mins , c ) 20 mins , d ) 25 mins , e ) 30 mins

Ex Output:

c