The correct answer is A) labyrinth. Labyrinth packing is primarily utilized to control steam leakage from the casing of a modern auxiliary turbine. Labyrinth seals are a type of non-contact seal that uses a series of small gaps or "labyrinths" to restrict the flow of steam, effectively preventing leakage. This design is well-suited for turbine applications as it can withstand high-pressure and high-temperature steam without direct contact between the moving and stationary components. The other options are incorrect because Teflon packing is more commonly used in low-pressure applications, dovetail packing is a type of mechanical seal, and carbon packing is typically used for other types of rotary equipment, not specifically for auxiliary turbines.