The correct response is: Both electric and magnetic fields are applied. Particles need to be charged.
In particle accelerators, electric fields are used to accelerate charged particles, while magnetic fields are employed to steer and focus the particles. To be effectively separated, the particles must have a charge, as the actions of the electric and magnetic fields depend on the particles interacting with those fields. Particles that are neutral (such as neutrons) would not be influenced by electric fields and would not be separated from charged particles in this manner.