How do passive diffusion, facilitated diffusion, and active transport differ in energy use and protein involvement?

How do passive diffusion, facilitated diffusion, and active transport differ in energy use and protein involvement?

• A. Passive diffusion uses energy and does not require transport proteins.
• B. Facilitated diffusion moves substances down their gradient using transport proteins; no energy required.
• C. Active transport uses energy to move substances against their gradient via pumps or co-transporters.
• D. Osmosis is the only form of passive diffusion and uses no energy.

Answer: (C)