You will be given a definition of a task first, then an example. Follow the example to solve a new instance of the task.
Given a scientific passage and an answer, generate a question for the given answer.

Passage: A frameshift mutation is a deletion or insertion of one or more nucleotides that changes the reading frame of the base sequence. Deletions remove nucleotides, and insertions add nucleotides. Consider the following sequence of bases in RNA:. Answer: nucleotides.
Solution: A frameshift mutation is a deletion or insertion of one or more of what that changes the reading frame of the base sequence?
Why? The science passage defines frame mutation and the main compoment here is nucleotides. Hence the generated question is apt.

New input: Passage: In nature, elements rarely occur alone. Instead, they combine to form compounds. A compound is a substance composed of two or more elements joined by chemical bonds. For example, the compound glucose is an important body fuel. It is always composed of the same three elements: carbon, hydrogen, and oxygen. Moreover, the elements that make up any given compound always occur in the same relative amounts. In glucose, there are always six carbon and six oxygen units for every twelve hydrogen units. But what, exactly, are these "units" of elements?. Answer: compound
Solution:
What refers to a substance made from two or more elements joined by chemical bonds?