Consider the following program:int main() { f1(); f2(2); f3(); return(0); } int f1() { return(1); } int f2(int X) { f3(); if (X==1) return f1(); else return (X*f2(X-1)); } int f3() { return(5); }Which one of the following options represents the activation tree corresponding to the main function?

An activation tree represents the function calls during the execution of a program, where each node corresponds to an activation of a procedure, the root is the activation of the main function, and the children of a node represent the procedure calls made by that activation in the chronological order of their calls (from left to right).

1. Root node (main):

   • main() sequentially calls:

     • First: f1()

     • Second: f2(2)

     • Third: f3()

   • Hence, main has three children from left to right: f1, f2, and f3.

2. Activation of f2(2):

   • Inside f2(2) (with $X = 2$):

     • It first calls f3().

     • Since $X \neq 1$, it enters the else branch and calls f2(1).

   • Thus, the node f2 (representing f2(2)) has two children: f3 and f2.

3. Activation of f2(1):

   • Inside f2(1) (with $X = 1$):

     • It first calls f3().

     • Since $X == 1$, it enters theif branch and calls f1().

   • Thus, this inner f2 node has two children: f3 and f1.

4. Neither f1() nor f3() makes any further calls, so their nodes are leaf nodes.

This call hierarchy precisely matches the tree shown in Option (A).