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 Q]: Problem: how many quarters are equal to 7 dollars ?
Options: a. 1, b. 28, c. 12, d. 9, e. 7
[EX A]: b

[EX Q]: Problem: four bells commence tolling together and toll at intervals of 2, 4, 6, 8 seconds respectively. in 18 minutes, how many times do they toll together ?
Options: a. 43, b. 44, c. 45, d. 46, e. 47
[EX A]: c

[EX Q]: Problem: the length of the bridge, which a train 140 metres long and travelling at 45 km / hr can cross in 30 seconds, is ?
Options: a. 255, b. 267, c. 235, d. 277, e. 211
[EX A]:
c