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: the total marks obtained by a student in mathematics and physics is 50 and his score in chemistry is 20 marks more than that in physics. find the average marks scored in mathamatics and chemistry together.
Options: a. 15, b. 25, c. 35, d. 45, e. 55

Ex Output:
c


Ex Input:
Problem: last year elaine spent 20 % of her annual earnings on rent. this year she earned 35 % more than last year and she spent 30 % of her annual earnings on rent. the amount she spent on rent this year is what percent of the amount spent on rent last year ?
Options: a. 202.5, b. 194.5, c. 197.5, d. 182.5, e. 177.5

Ex Output:
a


Ex Input:
Problem: a fair coin is tossed 5 times. what is the probability that it lands heads up at least twice ?
Options: a. 1 / 16, b. 5 / 16, c. 2 / 5, d. 13 / 16, e. 27 / 32

Ex Output:

d