The correct answer is C) machined metallic packing strips or fins. Labyrinth seals used to reduce leakage around a turbine shaft are typically constructed of machined metallic packing strips or fins. These metallic components create a tortuous path for the fluid flow, effectively reducing leakage without direct contact between the shaft and the seal. This design is preferred over options like rubber seals or braided asbestos, as the metallic construction is more durable and can better withstand the high temperatures and pressures associated with turbine shaft applications. The other answer choices, while potentially used in other sealing applications, are not the typical construction for labyrinth seals on turbine shafts.