Final answer:
A well-defined function must have a base case and move strictly closer to the base case.
Step-by-step explanation:
a. A well-defined function must have a base case, which is a precise but inaccurate set of measurements. This means that the initial condition of the problem is well-defined but may not accurately represent the desired outcome.
b. It is also important for a well-defined function to move strictly closer to the base case for all n > 1. This ensures that each step of the function brings us closer to the desired outcome.
c. Therefore, the correct answer is option c, which states that a well-defined function must have both a base case and move strictly closer to the base case.