Transpiration cooling differs from film cooling in that:

• A. Transpiration cooling uses coolant permeating the blade from inside; film cooling injects coolant at the surface to form a protective film.
• B. Film cooling uses coolant permeating inside; transpiration adds coolant only at the surface.
• C. They are identical processes with different terminology.
• D. Both rely on external air cooling without internal coolant.

Answer: (A)