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

[EX Q]: 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
[EX A]: What can be hard or even impossible to perform in a scientific sense?

[EX Q]: Passage: A lens that causes the light rays to bend away from its axis is called a diverging lens. Ray tracing is the technique of graphically determining the paths that light rays take. The image in which light rays from one point on the object actually cross at the location of the image and can be projected onto a screen, a piece of film, or the retina of an eye is called a real image. Thin lens equations are. Answer: diverging lens
[EX A]: What do you call a lens that causes the light rays to bend away from its axis?

[EX Q]: Passage: The most obvious landforms created by lava are volcanoes. These are mostly cinder cones, composite volcanoes, and shield volcanoes. Eruptions also take place through other types of vents, commonly from fissures ( Figure below ). The eruptions that created the entire ocean floor are essentially fissure eruptions. Answer: fissure eruptions
[EX A]:
Which type of eruptions created the entire ocean floor?