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

[EX Q]: Passage: Abundance The elements vary widely in abundance. In the universe as a whole, the most common element is hydrogen (about 90% of atoms), followed by helium (most of the remaining 10%). All other elements are present in relatively minuscule amounts, as far as we can detect. On the planet Earth, however, the situation is rather different. Oxygen makes up 46.1% of the mass of Earth's crust (the relatively thin layer of rock forming Earth's surface), mostly in combination with other elements, while silicon makes up 28.5%. Hydrogen, the most abundant element in the universe, makes up only 0.14% of Earth's crust. Table 2.1 "Elemental Composition of Earth" lists the relative abundances of elements on Earth as a whole and in Earth's crust. Table 2.2 "Elemental Composition of a Human Body" lists the relative abundances of elements in the human body. If you compare Table 2.1 "Elemental Composition of Earth" and Table 2.2 "Elemental Composition of a Human Body", you will find disparities between the percentage of each element in the human body and on Earth. Oxygen has the highest percentage in both Saylor URL: http://www. saylor. org/books. Answer: hydrogen
[EX A]: In the universe as a whole, what is the most common element?

[EX Q]: Passage: Sliding friction is friction that acts on objects when they are sliding over a surface. Sliding friction is weaker than static friction. That's why it's easier to slide a piece of furniture over the floor after you start it moving than it is to get it moving in the first place. Sliding friction can be useful. For example, you use sliding friction when you write with a pencil. The pencil "lead" slides easily over the paper, but there's just enough friction between the pencil and paper to leave a mark. Answer: sliding friction
[EX A]: What type of friction is friction that acts on objects when they are sliding over a surface?

[EX Q]: Passage: Liquid water is taken up by plant roots. The plant releases water vapor into the atmosphere. This is transpiration. Answer: transpiration
[EX A]:
What is it called when plant roots absorb liquid water and release water vapor into the atmosphere?