Question

Consider the following statements:
\[ S_1:\ \text{The sequence of procedure calls corresponds to a preorder traversal of the activation tree.} \] \[ S_2:\ \text{The sequence of procedure returns corresponds to a postorder traversal of the activation tree.} \] Which one of the following options is correct?

• A. \( S_1 \) is true and \( S_2 \) is false
• B. \( S_1 \) is false and \( S_2 \) is true
• C. \( S_1 \) is true and \( S_2 \) is true
• D. \( S_1 \) is false and \( S_2 \) is false

Hint:

Procedure calls follow preorder traversal, while procedure returns follow postorder traversal of the activation tree.

Answer 1

The Correct Option is C

Step 1: Meaning of an activation tree.
An activation tree captures the dynamic behavior of procedure calls during program execution. Each node represents a procedure invocation, and edges represent caller–callee relationships.

---

Step 2: Verification of Statement S₁.
A procedure is recorded in the execution trace at the moment it is invoked, before any of the procedures it calls are executed.

This order corresponds exactly to a preorder traversal of the activation tree.

Hence, S₁ is true.

---

Step 3: Verification of Statement S₂.
A procedure returns control to its caller only after all procedures it invoked have completed execution.

This behavior matches a postorder traversal of the activation tree.

Therefore, S₂ is also true.

---

Final Conclusion:
Since both statements S₁ and S₂ are correct, the appropriate answer is (C).