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: if x 2 + kx - 3, is divisible by ( x - 1 ), what is the value of k
Options: a. - 1, b. 1, c. 2, d. - 1, e. 0
[EX A]: c

[EX Q]: Problem: bottle r contains 350 capsules and costs $ 6.25. bottle t contains 130 capsules and costs $ 2.99. what is the difference between the cost per capsule for bottle r and the cost per capsule for bottle t ?
Options: a. $ 0.25, b. $ 0.12, c. $ 0.0052, d. $ 0.003, e. $ 0.002
[EX A]: c

[EX Q]: Problem: a boy swims downstream 48 km and upstream 12 km taking 6 hours each time; what is the speed of the current ?
Options: a. 1, b. 2, c. 3, d. 4, e. 5
[EX A]:
c