The graph illustrates how the rate of facilitated diffusion of substance X across a cell surface membrane altered as the concentration of substance X rose. Every condition other than the concentration of substance X was held constant. Temperature was kept at 15 ^{\circ}C. Which statement about the rate of facilitated diffusion is correct?
- AThe rate of facilitated diffusion of substance X at Q will increase if the temperature is increased to 20 ^{\circ}C.
- BThe rate of facilitated diffusion of substance X at P will increase if the concentration of ATP is increased.
- CThe rate of facilitated diffusion of substance X at Q will increase if the concentration of substance X is increased.
- DThe rate of facilitated diffusion of substance X at P will increase if the length of time over which the rate is measured is increased.