Extract the answer to the following question from the movie plot. If the question isn't answerable, please output "Can't answer". Question: What did the green crystal create? Title: Superman II Movie plot: Before the destruction of Krypton, the criminals General Zod (Terence Stamp), Ursa (Sarah Douglas) and Non (Jack O'Halloran) are sentenced to banishment into the Phantom Zone for insurrection and murder, amongst other crimes. Years later, the Phantom Zone is shattered near Earth by a shockwave stemming from the detonation of a hydrogen bomb, which had been launched into space by Superman (Christopher Reeve) after foiling a terrorist plot to blow up Paris. The three Kryptonian criminals are freed from the Zone, finding themselves with super-powers granted by the yellow light of Earth's sun. After attacking human astronauts on the Moon and the small town of East Houston, Idaho (which they mistake as being capital city of "Planet Houston" due to NASA's transmissions), the three criminals travel to the White House and force the President of the United States (E.G. Marshall) to kneel before General Zod, on behalf of the entire planet during an international television broadcast. When the President pleads for Superman to save the Earth, Zod demands that Superman come and "kneel before Zod!" Meanwhile, the Daily Planet sends Clark Kent and Lois Lane (Margot Kidder) to Niagara Falls. After Superman saves a little boy from falling into Niagara Falls, Lois wonders why Superman just happened to be in the area and suspects he and Clark are the same man. She dares Clark to admit he is Superman by jumping into the Niagara Falls river, but Clark saves her without exposing any of his abilities. That night, Clark accidentally falls into the room's fireplace, when trying to recover Lois's comb from the fire. When Lois discovers that his hand is unburned, Clark is forced to admit he is Superman. He takes her to his Fortress of Solitude in the Arctic, and shows her the traces of his past stored in the energy crystals of the fortress, one of which is the green crystal that created the Fortress and opened Superman's contact with his parents. Superman declares his love for Lois and his wish to spend his life with her. After...
The answer to this question is:
the Fortress