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

Passage: Experiments are sometimes hard or even impossible to do. For example, a scientist who is studying an extinct animal cannot experiment with the animal because it no longer exists. The scientist must rely instead on evidence in the natural world, such as fossils that the extinct animal left behind. Answer: experiments
What can be hard or even impossible to perform in a scientific sense?

Passage: Electron affinity is a measure of the energy released when an extra electron is added to an atom. Answer: electron affinity
What is the measure of the energy released when an extra electron is added to an atom?

Passage: But mining for gold is a slow, dirty, and dangerous process. Not everyone owns a gold mine in both the ancient Egyptian society and during the Roman Empire, the gold mines were the property of the state, not an individual or group. So there were few ways for most people to legally get any gold for themselves. Answer: state
In ancient egypt gold mines were the property of what?