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.

[Q]: Problem: the average of 11 10 prime numbers which are odd is ?
Options: a. 17.72, b. 18.52, c. 19.63, d. 16.53, e. 15.63
[A]: a

[Q]: Problem: the number of the members of a club is more than 50 and less than 80. when 4 people sit at a table, other people exactly divided to 8 - people groups ( 8 people sit at a table. or 7 - people groups ( 7 people sit at a table.. if the members are divided to 9 - people groups, how many people will be left ?
Options: a. 0, b. 2, c. 4, d. 6, e. 8
[A]: d

[Q]: Problem: if 2 tic equals 3 tacs and 2 tacs equal 7 tocs, what is the ratio of one tic to one toc ?
Options: a. 15 / 2, b. 6 / 5, c. 21 / 4, d. 3 / 10, e. 1 / 15
[A]:
c