Compact bone contains rings of osteons, each of which contains a central canal housing the blood vessels, which can be accessed only by those osteocytes adjacent to it. Gap junctions, which are tunnels between neighboring cells, then allow the cells that are not adjacent to the central canal to exchange nutrients and wastes with the bloodstream. Which statement is true about the exchange of materials with the bloodstream?

(A) Hydrophobic carbon dioxide waste must be passed via gap junctions from high concentration to low concentration.

(B) Hydrophilic Ca²⁺ is passed via gap junctions from low concentration to high concentration.

(C) Hydrophobic carbon dioxide waste does not require the gap junctions to travel from high concentrations to low concentrations.

(D) Hydrophilic Ca²⁺ does not require gap junctions to travel from high concentration to low concentrations.