With increasing ram effect.

• A. turbine temperatures decreases
• B. propulsive efficiency decreases
• C. propulsive efficiency increases
• D. engine weight increases

Answer: (C)

The concept here is how ram air from forward motion changes propulsion efficiency. When an aircraft moves faster, the air entering the engine has higher stagnation pressure—this ram rise pushes more pressure into the compressor without extra fuel or turbine work. That means, for the same thrust, the engine can deliver a lower exhaust jet velocity relative to the aircraft. Since propulsive efficiency improves when the jet velocity is closer to the aircraft’s speed (less kinetic energy is wasted in高速 exhaust relative to the air), increasing ram effect makes the propulsion system more efficient at converting fuel energy into forward thrust.

The other options don’t reliably describe the effect: ram rise isn’t guaranteed to lower turbine temperatures in a general sense, it doesn’t inherently reduce thrust-producing efficiency, and it doesn’t directly cause engine weight to increase.