Final answer:
The correct definition for I that is a well-defined function is f = {(a, 2), (b, 3), (c, 3), (d, 1)}.
Step-by-step explanation:
The correct definition for I that is a well-defined function is:
c. f = {(a, 2), (b, 3), (c, 3), (d, 1)}
A well-defined function must have a unique output for each input. In this case, each element in set A is paired with a unique element in set X, ensuring that there are no repeated inputs or outputs. The definition f = {(a, 2), (b, 3), (d, 1)} does not meet this criteria because the input 'b' is paired with two different outputs, (3) and (b, 3).