Which of the following items can be used to secure replacement pieces of wood during a gunstock repair?

The choice involving iron wire and heavy rubber bands is effective for securing replacement pieces of wood during a gunstock repair due to their strong grip and flexibility. Heavy rubber bands can provide a compressive force that holds the wood pieces tightly together, while iron wire can be manipulated to create custom shapes and wraps that further secure the wood without causing damage. This combination allows for adjustments and ease in positioning the replacement wood accurately while the adhesive sets, which is crucial in ensuring a strong and seamless repair.

Other options may not provide the same level of effectiveness or may introduce complications. For instance, rubber bands and nails may not offer enough stability, as rubber bands can degrade over time or may not hold the pieces firmly in place, leading to a poor bond. Twine and screws could secure pieces together but lack the even pressure and surface area contact needed for a reliable adhesive bond, which can result in a weak joint. Clamps and glue are indeed useful as they provide pressure and adhesive properties, but they require a tool to hold the pieces together, which may not be as accessible in all situations as the materials mentioned in choice C.