Diaphragm phrenic nerve

What is the role of the diaphragm during the process of inspiration?

1: The diaphragm expands, decreasing intrathoracic volume.
2: The diaphragm contracts, decreasing intrathoracic volume.
3: The diaphragm contracts, increasing intrathoracic volume.
4: The diaphragm expands, increasing intrathoracic volume.