Instruction Pipelining

Step 1: Identify common difficulties in instruction pipelining.
Instruction pipelining faces various difficulties that can cause it to deviate from its normal operation. These are typically caused by:

- **Resource conflicts (A):** Occurs when different pipeline stages require the same resource, causing delays in the pipeline.

- **Data dependency (C):** Happens when one instruction depends on the result of a previous instruction, which can delay the execution.

- **Branch difficulties (D):** Branch instructions can cause pipeline stalls as the pipeline may not know which instruction to fetch next until the branch condition is resolved.

Step 2: Explanation of other options.
- **Stack operation (B):** While stack operations are essential for certain computations, they are not typically listed as a major difficulty in pipelining, as they are handled by specific stages in the pipeline.

Step 3: Conclusion.
The correct answer is (3) A, C and D only, as these are the most significant difficulties in pipelining.