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

Example Input: Passage: outermost layer of the sun, made up of a plasma that extends millions of kilometers into space. Answer: plasma
Example Output: What is the outer layer of the sun made up of?

Example Input: Passage: Imagine walking in the forest in Figure below . The towering trees have been growing here for hundreds of years. It may seem as though the forest has been there forever. But no ecosystem is truly static. The numbers and types of species in most ecosystems change to some degree through time. This is called ecological succession. Important cases of ecological succession are primary succession and secondary succession. Answer: ecological succession
Example Output: The numbers and types of species in most ecosystems change to some degree through time and this is called?

Example Input: Passage: Light is a wave of changing electric and magnetic fields. Light waves are caused by disturbances in an electromagnetic field, like the acceleration of charged particles (such as electrons). Light has a dual nature; at times, it acts like waves, while at other times it acts like particles, called photons . Light travels through space at the maximum speed allowed by the laws of physics, called the speed of light. Light has no mass, but it carries energy and momentum. Fermat's principle states that light will always take the path that takes the least amount of time (not distance). Answer: light
Example Output:
Fermat's principle states that what will always take the path that takes the least amount of time?