Comets may come from a doughnut-shaped region beyond Neptune. What do scientist call this region?

Which is the best predictor of the radioactive nature of an isotope? o the proton-to-electron ratio the neutron-to-proton ratio o the neutron-to-electron ratio the electron-to-proton ratio

Which two particles are found in the center of an atom

What is the name of the perceived change in a sound wave’s frequency due to motion between the observer and the sound source?