Complex sentence: The Gotthard axis, consisting of the new Gotthard Base Tunnel, Zimmerberg Base Tunnel, Ceneri Base Tunnel, and surface connections, is being built under contract from the Swiss Federal Government by the company "AlpTransit Gotthard AG".
Split into simpler sentences: The Gotthard axis consists of the new Gotthard Base Tunnel, Zimmerberg Base Tunnel, Ceneri Base Tunnel, and surface connections. It is being built under contract from the Swiss Federal Government by the company "AlpTransit Gotthard AG".