Definition: In this task, you need to answer the given multiple-choice question on geometry. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.
Input: Problem: some students are standing in a circle in which 6 th and the 16 th student are standing opposite to each other . find how many students were present there .
Options: ['a ) 10', 'b ) 15', 'c ) 20', 'd ) 25', 'e ) 30']
Output:
c