Given a scientific passage and an answer, generate a question for the given answer.

Ex Input:
Passage: Avian Respiration Birds have evolved a respiratory system that enables them to fly. Flying is a high-energy process and requires a lot of oxygen. Furthermore, many birds fly in high altitudes where the concentration of oxygen in low. How did birds evolve a respiratory system that is so unique? Decades of research by paleontologists have shown that birds evolved from therapods, meat-eating dinosaurs (Figure 39.14). In fact, fossil evidence shows that meat-eating dinosaurs that lived more than 100 million years ago had a similar flow-through respiratory system with lungs and air sacs. Archaeopteryx and Xiaotingia, for example, were flying dinosaurs and are believed to be early precursors of birds. Answer: oxygen

Ex Output:
Birds have evolved a respiratory system that enables them to fly. flying is a high-energy process and requires a lot of this?

Ex Input:
Passage: One useful application of PET scanning is in the diagnosis of Alzheimer's disease. This debilitating condition associated with memory loss primarily occurs in elderly individuals. A protein known as beta-amyloid gradually forms deposits, or plaques, in the brain. Severe memory loss and impaired movement appear to be direct results of the plaque growth. Answer: elderly

Ex Output:
Alzheimers disease is associated with memory loss in what group of people?

Ex Input:
Passage: 4. Molecular crystals -- Molecular crystals typically consist of molecules at the lattice points of the crystal, held together by relatively weak intermolecular forces (see Figure below ). The intermolecular forces may be dispersion forces in the case of nonpolar crystals, or dipole-dipole forces in the case of polar crystals. Some molecular crystals, such as ice, have molecules held together by hydrogen bonds. When one of the noble gases is cooled and solidified, the lattice points are individual atoms rather than molecules. In all cases, the intermolecular forces holding the particles together are far weaker than either ionic or covalent bonds. As a result, the melting and boiling points of molecular crystals are much lower. Lacking ions or free electrons, molecular crystals are poor electrical conductors. Answer: molecular crystals

Ex Output:
What crystals consist of molecules at the lattice points of the crystal, held together by relatively weak intermolecular forces?