In this task, you need to provide the correct option for a given problem from the provided options.

Ex Input:
Problem: teas worth rs . 126 per kg and rs . 135 per kg are mixed with a third variety in the ratio 1 : 1 : 2 . if the mixture is worth rs 156 per kg , the price of the third variety per kg will be ?
Options: a ) rs . 147.50 , b ) rs . 785.50 , c ) rs . 178.50 , d ) rs . 258.50 , e ) none of these

Ex Output:
c

Ex Input:
Problem: the compound ratio of 5 : 6 , 3 : 2 and 4 : 5 is ?
Options: a ) 3 : 5 , b ) 2 : 7 , c ) 1 : 1 , d ) 1 : 4 , e ) none

Ex Output:
c

Ex Input:
Problem: tough and tricky questions : ratios 4 / 5 of a certain class left on a field trip . 1 / 3 of the students who stayed behind did not want to go on the field trip ( all the others did want to go ) . when another vehicle was located , 1 / 2 of the students who did want to go on the field trip but had been left behind were able to join . what fraction of the class ended up going on the field trip ?
Options: a ) 1 / 2 , b ) 2 / 3 , c ) 13 / 15 , d ) 23 / 30 , e ) 4 / 5

Ex Output:
c