Final answer:
The common shielding gases for GTAW are Argon and Helium, both of which provide an inert atmosphere necessary for clean and uncontaminated welding.
Step-by-step explanation:
The common shielding gases used for the Gas Tungsten Arc Welding (GTAW) process are: A) Argon and D) Helium. Both argon and helium are noble gases, known for their lack of reactivity, which makes them ideal for creating an inert atmosphere during the welding process to protect the weld area from contamination. Argon possesses lower heat conductivity, which helps in maintaining stability in the arc during welding and is preferable to nitrogen for preventing vaporization of the material being welded. Helium, on the other hand, has the benefit of producing a hotter arc, which can be desirable for welding thicker materials.