Computer Architecture

Step 1: Understanding Stack-Organised Computers.
A stack-organised computer uses a stack to hold its operands and results. Instructions typically manipulate the stack and use a Last-In-First-Out (LIFO) order.

Step 2: Instruction Formats.
- Zero-Address Instructions: In this format, no operands are explicitly provided in the instruction. The operands are implicitly taken from the stack, and the result is placed back on the stack. This is the most common format used in stack-organised computers.
- One-Address Instructions: These require one operand to be explicitly specified, with the other operand implicitly taken from the stack.
- Two-Address Instructions: This format requires two explicit operands. It is typically used in register-based or accumulator-based computers.
- Three-Address Instructions: This format specifies three operands, often used in complex processors.

Step 3: Conclusion.
The correct answer is (A) Zero-Address Instructions, as stack-organised computers operate on a stack and typically use zero-address instructions.