The following code will generate a compiler error.

string GetAgePhrase(int age) {
    if (age > 60) return "Senior";
    if (age > 40) return "Middle-aged";
    if (age > 20) return "Adult";
    if (age > 12) return "Teen-aged";
    if (age > 4) return "Toddler";
}

Which of the following statements, inserted as the last line of the function, would solve the problem?