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.

Example Input: Problem: if a certain coin is flipped, the probability that the coin will land heads is 1 / 2. if the coin is flipped 6 times, what is the probability that it will land heads up on the first 4 flips but not on the last 2 flips ?
Options: a. 1 / 8, b. 1 / 16, c. 1 / 32, d. 1 / 64, e. 1 / 128
Example Output: d

Example 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
Example Output: c

Example Input: Problem: at a school, 3 - fifths of the male students and two - thirds of the female students speak a foreign language. if the number of males is equal to the number of females, what fraction of the students speak a foreign language ?
Options: a. 17 / 30, b. 19 / 30, c. 11 / 15, d. 7 / 15, e. 2 / 5
Example Output:
b