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: what is the value of n if the sum of the consecutive odd intergers r from 1 to n equals 169 ?
Options: a. 47, b. 25, c. 37, d. 33, e. 29

Ex Output:
b

Ex Input:
Problem: excluding the stoppages, the speed of a bus is 48 km / hr and including the stoppages the speed of the bus is 12 km / hr. for how many minutes does the bus stop per hour ?
Options: a. 45 min, b. 10 min, c. 12 min, d. 20 min, e. 18 min

Ex Output:
a

Ex Input:
Problem: employees of a certain company are each to receive a unique 10 - digit identification code consisting of the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9 such that no digit is used more than once in any given code. in valid codes, the second digit in the code is exactly twice the first digit. how many valid codes are there ?
Options: a. 145,660, b. 149,720, c. 155,420, d. 161,280, e. 167,480

Ex Output:
d