Which of These Is an Example of Active Transport

Multiple Choice

Which of these is an example of active transport?

A) Diffusion of oxygen from a place of high concentration to a place of lower concentration
B) Facilitated diffusion of K⁺
C) Transport of glucose down its concentration gradient
D) Transport of Na⁺ from a place of low concentration to a place of higher concentration
E) Transport of Cl^- following its concentration gradient