What is the purpose of valve overlap in a four-stroke internal combustion engine?

1. To allow a small amount of fuel to escape through the exhaust valve to cool the manifold.
2. To utilize the momentum of the incoming fresh charge and outgoing exhaust gases to improve scavenging and volumetric efficiency.
3. To increase the compression ratio of the engine by closing both valves late.
4. To prevent the piston from hitting the valves at high engine speeds.