Movement of substances into the cell is largely dependent on the size, polarity, and concentration gradient of the substance. Which of the following represents an example of active transport of a substance into a cell?
(A) Diffusion of oxygen into erythrocytes (red blood cells) in the alveolar capillaries of the lungs
(B) Influx of sodium ions through a voltage-gated ion channel in a neuron cell during an action potential
(C) The sodium-potassium pump, which restores resting membrane potentials in neurons through the use of ATP
(D) Osmosis of water into an epithelial cell lining the lumen of the small intestine