During the last few years, the fuel expense of running a jet aircraft has fallen. In the same period, better design has produced aircraft that are far less noisy. How would this change the marginal private cost (MPC) and the marginal external cost (MEC) of air travel?
- Aa downward shift of both the MPC and the MEC curves
- Ba downward shift of the MPC curve and a movement left along the MEC curve
- Ca movement left along both the MPC and the MEC curves
- Da movement left along the MPC curve and a downward shift of the MEC curve