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 a person walks at 25 km / hr instead of 10 km / hr, he would have walked 20 km more. the actual distance traveled by him is :
Options: a. 50 km, b. 56 km, c. 13.3 km, d. 70 km, e. 80 km

Ex Output:
c


Ex Input:
Problem: 18.05 ã — 0.001 = ?
Options: a. 0.1805, b. 0.01805, c. 1.805, d. 0.001805, e. none of these

Ex Output:
b


Ex Input:
Problem: in x - y plane, there is a right triangle abc ( ∠ b = 90 o ). if the length of ac is 25 and the slope of line segment ac is 4 / 3, what is the length of ab ?
Options: a. 12, b. 18, c. 24, d. 20, e. 40

Ex Output:

d