A piston traps air in a cylinder. The air has pressure $p$, and the air column measures $20\,\text{cm}$ in length. The piston is drawn outwards until the length of the air column has increased by $40\,\text{cm}$. The temperature of the air stays constant. What is the new air pressure?
- A$\frac{p}{2}$
- B$\frac{p}{3}$
- C$2p$
- D$3p$