Consider the program given below, in a block-structured pseudo-language with lexical scoping and nesting of procedures permitted.Program main; Var ... Procedure A1; Var ... Call A2; End A1 Procedure A2; Var ... Procedure A21; Var ... Call A1; End A21 Call A21; End A2 Call A1; End main.Consider the calling chain: Main $\rightarrow$ A1 $\rightarrow$ A2 $\rightarrow$ A21 $\rightarrow$ A1 The correct set of activation records along with their access links is given by

In a block-structured language with lexical (static) scoping, an activation record's access link (or static link) points to the activation record of its immediate enclosing lexical scope (the procedure where it is statically declared), not the caller.

Let's analyze the lexical nesting in the given code:

• main is the outermost program scope.

• Procedure A1 is declared inside main, so any activation of A1 has its access link pointing to the activation record of main [d1].

• Procedure A2 is declared inside main, so any activation of A2 has its access link pointing to main [d1].

• Procedure A21 is declared inside A2, so any activation of A21 has its access link pointing to A2 [d1].

For the calling sequence $\text{Main} \rightarrow \text{A1} \rightarrow \text{A2} \rightarrow \text{A21} \rightarrow \text{A1}$:

1. $\text{Main}$: Base activation record.

2. $\text{A1}$ (called by $\text{Main}$): Access link $\rightarrow \text{Main}$.

3. $\text{A2}$ (called by $\text{A1}$): Access link $\rightarrow \text{Main}$.

4. $\text{A21}$ (called by $\text{A2}$): Access link $\rightarrow \text{A2}$.

5. $\text{A1}$ (called by $\text{A21}$): Access link $\rightarrow \text{Main}$.

This exact configuration of access links corresponds to option (D) [d1].