The correct answer is C) an inadequate supply of oxygen. Asphyxia is a condition that arises from a lack of oxygen reaching the body's tissues. This can occur due to various reasons, such as obstruction of the airway, drowning, or being in an environment with insufficient oxygen. An inadequate supply of oxygen is the direct cause of asphyxia, as the body requires a continuous supply of oxygen to function properly. The other options, such as too much oxygen, improper caloric intake, or sleep deprivation, are not the primary causes of asphyxia.