Detailed Instructions: Given a scientific passage and an answer, generate a question for the given answer.
See one example below:
Problem: 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?
Explanation: The science passage defines frame mutation and the main compoment here is nucleotides. Hence the generated question is apt.

Problem: Passage: Blood vessels are long, tube-like organs that form a complex network throughout the body. They transport blood to all the body's cells. There are three types of blood vessels: arteries, veins, and capillaries. Transfer of substances between the blood and cells takes place across the thin walls of capillaries. Answer: capillaries
Solution:
Arteries and veins are two of the three types of blood vessels, what is the third?