Air is enclosed in a cylinder by means of a piston. The air has pressure $p$ and the air column has a length of $20\,\text{cm}$. The piston is pulled outwards. As a result, the length of the air column increases 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$3p$