Answer: (iv) Lexical program structure

Explanation

In static (lexical) scoping, a variable reference is bound to the declaration found by looking at the textual nesting of blocks/procedures in the source code: first the innermost enclosing block, then the next one outward, and so on.

• The binding can be decided at compile time, without running the program.
• The call sequence at run time (option i) decides the binding only in dynamic scoping.
• Registers (ii) and heap location (iii) have nothing to do with name resolution.

int x = 10;
void f() { printf("%d", x); }   // x refers to the global x
void g() { int x = 20; f(); }   // still prints 10 under static scoping

$$\boxed{\text{(iv)}}$$