You will be given a definition of a task first, then some input of the task.
Given a scientific passage and an answer, generate a question for the given answer.

Passage: One way to prevent corrosion is to protect the surface of the metal. Covering the surface of the metal object with paint or oil will prevent corrosion by not allowing oxygen to contact it. Unfortunately, scratches in the paint or wearing off of the oil will allow the corrosion to begin. Corrosion-sensitive metals can also be coated with another metal that is resistant to corrosion. A "tin can" is actually made of iron coated with a thin layer of tin which protects the iron. Answer: corrosion
Output:
Protecting the surface of metal prevents what?