Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.

Ex Input:
Problem: two trains of equal length are running on parallel lines in the same directions at 46 km / hr. and 36 km / hr. the faster trains pass the slower train in 72 seconds. the length of each train is :
Options: a. 82 m, b. 50 m, c. 72 m, d. 100 m, e. none of these

Ex Output:
d


Ex Input:
Problem: a bottle contains a certain solution. in the bottled solution, the ratio of water to soap is 3: 4, and the ratio of soap to salt is five times this ratio. the solution is poured into an open container, and after some time, the ratio of water to soap in the open container is halved by water evaporation. at that time, what is the ratio of water to salt in the solution ?
Options: a. 9: 32, b. 9: 30, c. 32: 9, d. 19: 32, e. 18: 30

Ex Output:
a


Ex Input:
Problem: bruce and anne can clean their house in 4 hours working together at their respective constant rates. if anne ’ s speed were doubled, they could clean their house in 3 hours working at their respective rates. how many w hours does it currently take anne to clean the house on her own ?
Options: a. 6, b. 7, c. 8, d. 12, e. 14

Ex Output:

d