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

Ex Input:
Passage: the fact that stars are made up of very lightweight hydrogen gas. Answer: hydrogen

Ex Output:
What type of gas are stars made up of?

Ex Input:
Passage: The stoichiometry of a reaction describes the relative amounts of reactants and products in a balanced chemical equation. A stoichiometric quantity of a reactant is the amount necessary to react completely with the other reactant(s). If a quantity of a reactant remains unconsumed after complete reaction has occurred, it is in excess. The reactant that is consumed first and limits the amount of product(s) that can be obtained is the limiting reactant. To identify the limiting reactant, calculate the number of moles of each reactant present and compare this ratio to the mole ratio of the reactants in the balanced chemical equation. The maximum amount of product(s) that can be obtained in a reaction from a given amount of reactant(s) is the theoretical yield of the reaction. The actual yieldis the amount of product(s) actually obtained in the reaction; it cannot exceed the theoretical yield. The percent yield of a reaction is the ratio of the actual yield to the theoretical yield, expressed as a percentage. Answer: in excess

Ex Output:
If a quantity of a reactant remains unconsumed after complete reaction has occurred, it is?

Ex Input:
Passage: Millions of fossils have been found since Darwin's time. They show that evolution may occur in fits and starts. Long period of little or gradual change may be interrupted by bursts of rapid change. The rate of evolution is influenced by how the environment is changing. Today, Earth's climate is changing rapidly. How do you think this might affect the rate of evolution?. Answer: evolution

Ex Output:
Fossil records show that what process may occur in "fits and starts"?