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 thief is spotted by a policeman from a distance of 150 meters. when the policeman starts the chase, the thief also starts running. if the speed of the thief be 8 km / hr and that of the policeman 10 km / hr, how far the thief will have run before he is overtaken ?
Options: a. 350 m, b. 200 m, c. 400 m, d. 600 m, e. none of them

Ex Output:
d

Ex Input:
Problem: how many positive even integers less than 100 contain digits 5 or 7 ?
Options: a. 10, b. 17, c. 18, d. 19, e. 20

Ex Output:
a

Ex Input:
Problem: huey ' s hip pizza sells two sizes of square pizzas: a small pizza that measures 12 inches on a side and costs $ 10, and a large pizza that measures 18 inches on a side and costs $ 20. if two friends go to huey ' s with $ 30 apiece, how many more square inches of pizza can they buy if they pool their money than if they each purchase pizza alone ?
Options: a. 5 square inches, b. 36 square inches, c. 15 square inches, d. 25 square inches, e. 350 square inches

Ex Output:
b