Given a scientific question, generate a correct answer to it.

Input: Consider Input: What is the smallest particle of an element that still has the properties of that element is called?

Output: atom

Input: Consider Input: What is formed when nitrogen and sulfur oxides dissolve in rain?

Output: acid rain

Input: Consider Input: The as yet undiscovered grand unified theory is a search to unify laws of what branch of science?
Output: physics