The answer to your question would be D
ATP production would be stimulated. Positive feedback basically just enhances an original stimuli, so for example, blood clotting usually occurs at a lower rate. But when there is an injury, that blood clotting stimuli is enhanced to keep producing a large clot to make sure the wound is covered.
C) K ( potassium)
Explanation:
Small non-charged molecules like CO2, H2O, O2 can pass through the membrane freely.
But others such as K+ require specific potassium bumps throughout the membrane. Which acts to transport Na+ and K+ cross the membrane.