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

Passage: Most chemical reactions in organisms take place in an environment that is mostly water. Answer: water
The environment where most chemical reactions in organisms takes place consists mostly of what?

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

Passage: Volcanic eruptions can be devastating, particularly to the people who live close to volcanoes. Volcanologists study volcanoes to be able to predict when a volcano will erupt. Many changes happen when a volcano is about to erupt. Answer: volcanologists
Who study volcanoes to be able to predict when a volcano will erupt?