What is a key feature of recursive functions?

A key feature of recursive functions is that they require a termination condition to prevent infinite calls. In recursion, a function calls itself to solve smaller subproblems of the same type, and without a proper base case or termination condition, this could lead to an infinite loop. When the base case is met, the function stops calling itself, which allows the program to complete its execution and return results. This property is essential for ensuring that recursion resolves the problem instead of perpetuating itself endlessly.

The other aspects mentioned in the options do not define recursive functions accurately. For instance, optimizing data storage is more relevant to algorithms that manage resources efficiently, rather than a defining characteristic of recursion. Similarly, converting data into machine language pertains to compilation and interpretation processes, not specifically to recursion. Managing user input is also a general programming concept that can apply to many programming constructs but isn't uniquely tied to the principles of recursion.