Answer the following question given this paragraph: 

Scientists have built machines called particle accelerators . These amazing tools smash particles that are smaller than atoms into each other head-on. This creates new particles. Scientists use particle accelerators to learn about nuclear fusion in stars. They can also learn about how atoms came together in the first few minutes of the Universe. Two well-known accelerators are SLAC, in California, and CERN, in Switzerland ( Figure below ).


Q: What machines have scientist built to smash particles that are smaller than atoms into each other head-on?

 Choices:

- energy accelerators

- nitrogen accelerators

- Atom Accelerators

- particle accelerators

A:
particle accelerators
