Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Input: Passage: Some comets have periods of thousands or even millions of years. Most long-period comets come from a very distant region of the solar system. This region is called the Oort cloud. The Oort cloud is about 50,000100,000 times the distance from the Sun to Earth. Answer: oort cloud
Output:
What is the name of the cloud where most long-period comets come from?