(A) When the valve of a bicycle tube is opened,the compressed air inside the tube expands rapidly to the outside atmosphere. This process occurs so quickly that there is no time for heat exchange with the surroundings,making it an adiabatic process. According to the first law of thermodynamics,$dQ = dU + dW$. Since the process is adiabatic,$dQ = 0$,which implies $dU = -dW$. As the air does work $(dW > 0)$ in expanding against the external atmospheric pressure,its internal energy $(dU)$ decreases. Since the internal energy of an ideal gas is directly proportional to its temperature,the decrease in internal energy leads to a drop in temperature,making the escaping air feel cold.