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: a 24 ' ' x 24 ' ' square metal plate needs to be fixed by a carpenter on to a wooden board. the carpenter uses nails all along the edges of the square such that there are 25 nails on each side of the square. each nail is at the same distance from the neighboring nails. how many nails does the carpenter use ?
Options: ['a. 94', 'b. 95', 'c. 96', 'd. 97', 'e. 98']

Ex Output:
c


Ex Input:
Problem: in what time will a railway train 50 m long moving at the rate of 36 kmph pass a telegraph post on its way ?
Options: a. 5 sec, b. 4 sec, c. 3 sec, d. 6 sec, e. 1 sec

Ex Output:
a


Ex Input:
Problem: pipe p can fill a tank in 3 hours, pipe q in 9 hours and pipe r in 18 hours. if all the pipes are open, in how many hours will the tank be filled ?
Options: a. 2 hours, b. 2.4 hours, c. 3 hours, d. 3.5 hours, e. 4.5 hours

Ex Output:

a