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 can finish a work in 60 days, b in 9 days and c in 2 days, b and c start the work but are forced to leave after 3 days. the remaining work was done by a in ?
Options: a. 10 days, b. 25 days, c. 6 days, d. 7 days, e. 8 days

Ex Output:
b

Ex Input:
Problem: a fort had provision of food for 150 men for 45 days. after 15 days, 10 men left the fort. the number of days for which the remaining food will last, is :
Options: a. 32, b. 37 1 / 4, c. 42, d. 54, e. 45

Ex Output:
a

Ex Input:
Problem: the average weight of 29 students is 28 kg. by the admission of a new student, the average weight is reduced to 27.1 kg. the weight of the new student is
Options: a. 22 kg, b. 1 kg, c. 22.4 kg, d. 21 kg, e. none of these

Ex Output:
b