Generate a question with a factual answer.
Generated: What selling methods did the Marble Palace use?

Generate a question with a factual answer.
Generated: What kind of process is the zinc zinc-oxide cycle?

Generate a question with a factual answer.
Generated: How long should the plastic bottles filled with water be exposed to sunlight during Solar water disinfection?

Generate a question with a factual answer.
Generated: What is the second question to ask in order to define the two classes?