What is the function of the tractor’s middle lift arm (“the third point”)?

1. A To prevent vertical freedom of movement of the arms and of the tool.
2. B To secure the harnessed tool with special security chains.
3. C To prevent sideways freedom of movement of the arms and to prevent the tractor turning.
4. D To lift the tool a few times to maximum height in order to ensure that the tool is properly harnessed.