A. Active transport
B. Simple diffusion
C. Facilitated diffusion
D. Protein channel
参考答案:
C
本题详细解析:
Facilitated diffusion occurs with the help of protein channels or carrier proteins.
Active transport (Choice A) requires energy expenditure in the form of ATP and moves substances up their concentration gradient. Simple diffusion (Choice B) occurs through the cell membrane without the use of membrane proteins. Protein channels (Choice D) often carry out facilitated diffusion, but they are not themselves a type of transport.
