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: if julie rows 32 km upstream and 72 km down steam taking 4 hours each, then the speed of the stream
Options: a. 1.5 kmph, b. 0.5 kmph, c. 0.4 kmph, d. 1.6 kmph, e. 2.5 kmph

Ex Output:
b


Ex Input:
Problem: what is the tens digit of 6 ^ 10 ?
Options: a. 7, b. 3, c. 5, d. 1, e. 9

Ex Output:
a


Ex Input:
Problem: fresh grapes contain 80 % water by weight and raisins obtained by drying fresh grapes contain 25 % water by weight. how many kgs of fresh grapes are needed to get 40 kgs of raisins ?
Options: a. 150 kgs, b. 64 kgs, c. 72 kgs, d. 65 kgs, e. 70 kgs

Ex Output:

a