Detailed Instructions: In this task, you need to answer the given multiple-choice question on geometry. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.
Problem:Problem: twenty - one dots are evenly spaced on the circumference of a circle . how many combinations of three dots can we make from these 21 dots that do not form an equilateral triangle ?
Options: ['a ) 1299', 'b ) 1305', 'c ) 1311', 'd ) 1317', 'e ) 1323']
Solution:
e