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 clock shows the time as 9 a. m. if the minute hand gains 7 minutes every hour, how many minutes will the clock gain by 6 p. m. ?
Options: a. 30 min, b. 35 min, c. 63 min, d. 50 min, e. 55 min

Ex Output:
c

Ex Input:
Problem: a solid yellow stripe is to be painted in the middle of a certain highway. if 1 gallon of paint covers an area of q square feet of highway, how many gallons of paint will be needed to paint a stripe of t inches wide on a stretch of highway m miles long ? ( 1 mile = 5,280 feet and 1 foot = 12 inches )
Options: ['a. ( 5,280 mt ) / 12 q', 'b. ( 5,280 pt ) / 12 m', 'c. ( 5,280 pmt ) / 12', 'd. ( 5,280 ) ( 12 m ) / pt', 'e. ( 5,280 ) ( 12 p ) / mt']

Ex Output:
a

Ex Input:
Problem: of the seven - digit positive integers that have no digits equal to zero, how many have two digits that are equal to each other and the remaining digit different from the other two ?
Options: a. 24, b. 36, c. 72, d. 152409600, e. 216

Ex Output:
d