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 question, generate a correct answer to it.

Who proposed the theory of evolution by natural selection?
Solution: darwin
Why? This is a direct fact that Charles Darwin proposed the theory of evolution.

New input: What state of matter is like a liquid in that particles are in contact with each other, but unlike liquids in that the intermolecular forces are strong enough to hold the particles in place?
Solution:
solids