Whether Sleeping or Exercising,the Rate of Gas Exchange Is Precisely

Multiple Choice

Whether sleeping or exercising,the rate of gas exchange is precisely matched to the body's immediate respiratory needs;gas exchange during exercise,for example,increases because

A) when muscle contracts,the adjacent capillaries are compressed,forcing the gases out and into the surrounding tissues.
B) active cells are warmer than resting cells.
C) the rate of diffusion is proportional to the gas concentration gradients that are high during exercise and low during rest.
D) the elevated blood pressures during activity expands the capillaries,which increases the surface area available for gas exchange.