upper atmospheric disturbances. the tilt of Earth's rotational axis. density differences caused by temperature changes. the gravitational pull of the Sun and the Moon.
I gave my students this multiple choice question: Tides occur in the oceans at regular times every day because of

Only one answer is correct among these 4 choices:
- upper atmospheric disturbances.
- the tilt of Earth's rotational axis.
- density differences caused by temperature changes.
- the gravitational pull of the Sun and the Moon.

Could you tell me which one is correct?

the gravitational pull of the Sun and the Moon.