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

Ex Input:
Passage: The largest known virus, called mimivirus, is so large that scientists first mistook it for a bacterium. It was first discovered in amoeba, in 1992, and was identified as a virus in 2003. Scientists believe that mimivirus may cause certain types of pneumonia in humans. The core contains DNA, with the majority of the DNA in genes, and only 10% DNA of unknown function ("junk" DNA). Answer: mimivirus

Ex Output:
What is the largest known virus?

Ex Input:
Passage: Chemistry is based on the modern atomic theory, which states that all matter is composed of atoms. Answer: chemistry

Ex Output:
What branch of science is based on the modern atomic theory, which states that all matter is composed of atoms?

Ex Input:
Passage: Currents also flow deep below the surface of the ocean. Deep currents are caused by differences in density at the top and bottom. Density is defined as the amount of mass per unit of volume. More dense water takes up less space than less dense water. It has the same mass but less volume. Water that is more dense sinks. Less dense water rises. What can make water more dense?. Answer: density

Ex Output:
Deep ocean currents are caused by differences in what property at the top and bottom?