Which of the following actions should not be performed on floor joists or rafters?

When considering actions that should not be performed on floor joists or rafters, it's important to recognize how notching can affect the structural integrity of these components. Notching in the center third of a span is problematic because this area is under the most stress; modifying it can significantly weaken the joist or rafter. Similarly, notching in the outer third of the span is also inadvisable, as it can compromise the material's capacity to transfer loads appropriately, leading to potential structural issues.

Drilling holes that do not exceed one-third of the depth is generally acceptable because it minimizes the risk of compromising the joist's strength, as long as the holes are properly positioned and within safe guidelines. Therefore, options A and C both represent actions that should be avoided on floor joists and rafters, supporting the choice that both are inappropriate to undertake. This understanding is crucial for maintaining the integrity and safety of structural elements in construction.