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.

Problem: what is the greatest positive integer n such that 3 ^ n is a factor of 36 ^ 100 ?
Options: a. 100, b. 200, c. 300, d. 600, e. 900
b

Problem: the population of a town increases 25 % and 40 % respectively in two consecutive years. after the growth the present population of the town is 1750. then what is the population of the town 2 years ago ?
Options: a. a. 750, b. b. 800, c. c. 850, d. d. 900, e. e. 950
b

Problem: a cistern 5 m long and 4 m wide contains water up to a depth of 1 m 25 cm. the total area of the wet surface is :
Options: a. 49 m 2, b. 42.5 m 2, c. 53.5 m 2, d. 55 m 2, e. 57 m 2
b