What is an important feature of recursion?

An important feature of recursion is that it typically has a base case to ensure it terminates. The base case acts as a stopping point for the recursive calls, preventing infinite loops and eventually allowing the function to return a result. This fundamental aspect of recursion allows it to divide a problem into smaller subproblems, solving each one until it reaches the base case. For instance, in a factorial calculation, the base case would be when the input number is zero, at which point the function would return one, thereby facilitating the resolution of the recursive calls that led to that point.

Without a proper base case, a recursive function could lead to excessive, never-ending calls, which would result in a stack overflow error as the call stack exceeds its limit. In contrast, the other options suggest features or limitations that don't apply to recursion; loops are not a necessity for it to function, recursion is not limited to integers, and efficiency comparisons between recursion and iterative methods depend on the specific use case rather than being an inherent characteristic of recursion itself.