Fact 1: The gravitational pull of the Moon on Earth 's oceans causes the tides.

Fact 2: Planetary moons are natural satellites.

Given the two facts above, answer the question "The pull of what on the Earth's oceans cause the tides?" with the following options: 
- A yellow star
 - Time and energy
 - energy of moving objects
 - A natural satellite
 - flow of electrons
 - An artificial satellite
 - A red star
 - hydrogen and oxygen


 

    A natural satellite     