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'.
Input: Problem: when the circumference and area of a circle are numerically equal , then the diameter is numerically equal to
Options: ['a ) area', 'b ) circumference', 'c ) 4', 'd ) 2 ', 'e ) none of these']
Output:
c