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: 1391 x 1391 = ?
Options: a. a. 1951609, b. b. 1951601, c. c. 1951602, d. d. 1951603, e. e. 1934881
[EX A]: e

[EX Q]: Problem: what is the units digit of ( 3 ^ 13 ) ( 4 ^ 13 ) ?
Options: a. 2, b. 4, c. 6, d. 7, e. 8
[EX A]: a

[EX Q]: Problem: a boat having a length 3 m and breadth 2 m is floating on a lake. the boat sinks by 2 cm when a man gets on it. the mass of man is
Options: a. 12 kg, b. 60 kg, c. 72 kg, d. 120 kg, e. none
[EX A]:
d