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.

Example Input: Problem: a boat having a length 8 m and breadth 2 m is floating on a lake. the boat sinks by 1 cm when a man gets on it. the mass of the man is :
Options: a. 12 kg, b. 60 kg, c. 72 kg, d. 160 kg, e. none of these
Example Output: d

Example Input: Problem:. 005 / ? =. 01
Options: a.. 5, b.. 05, c.. 005, d.. 0005, e. none of them
Example Output: a

Example Input: Problem: if the sum of two numbers is 45 and the h. c. f and l. c. m of these numbers are 4 and 5 respectively, then the product of the reciprocals is equal to :
Options: a. 20 / 20, b. 1 / 1, c. 2 / 30, d. 11 / 20, e. 1 / 20
Example Output:
e