- The tide is when ocean levels periodically rise / fall
- The gravitational pull of the moon on earth 's oceans causes the tides
- So, the gravitational pull causes the ocean levels on earth to rise and fall periodically

So, the gravitational pull causes the ocean levels on earth to rise and fall periodically
Q: Which of the following is a cause of the ocean levels periodically rising and then falling?
Context:
- The tide is when ocean levels periodically rise / fall 
- The gravitational pull of the moon on earth 's oceans causes the tides