During each cycle of normal resting ventilation, a volume of gas is moved into and out of the respiratory tract. This cyclical volume is called the:

a. inspiratory reserve volume (IRV).
b. vital capacity (VC).
c. residual volume (RV).
d. tidal volume (VT).

ANS: D
During each cycle, a volume of gas moves in and out of the respiratory tract. This volume, meas-ured during either inspiration or expiration, is called the tidal volume, or VT.