Foundation skill check: In AP CSA, this item is specifically about Recursion: primitive types, using objects, boolean expressions, iteration. Identify the base case in a recursive method that calculates the factorial of $n$. Provide the solution as code.

Foundation skill check: In AP CSA, this item is specifically about Recursion: primitive types, using objects, boolean expressions, iteration. What is the result of mystery(3) if mystery(n) is n + mystery(n-1) with base case mystery(0) = 0? Provide the solution as code.

Foundation skill check: In AP CSA, this item is specifically about Recursion: primitive types, using objects, boolean expressions, iteration. Explain what happens if a recursive method never reaches a base case. Provide the solution as code.

Foundation skill check: In AP CSA, this item is specifically about Recursion: primitive types, using objects, boolean expressions, iteration. Trace f(123) for void f(int n) { if (n > 0) { f(n/10); System.out.print(n%10); } }. Provide the solution as code.

Foundation skill check: In AP CSA, this item is specifically about Recursion: primitive types, using objects, boolean expressions, iteration. In a recursive binary search, what happens to the search range in each step? Provide the solution as code.

Foundation skill check: In AP CSA, this item is specifically about Recursion: primitive types, using objects, boolean expressions, iteration. How many recursive calls are made to calculate fib(4) using the standard recursive Fibonacci formula? Provide the solution as code.