Available choices:
1). tides;
2). waves;
3). heat;
4). gravitational pull of the sun;
5). rain;
6). the world's orbit;
7). motion;
8). erosion;

Fact 1: The gravitational pull of the Moon on Earth 's oceans causes the tides. Fact 2: Earth Day celebrations are now held across the world. Given the two facts above, what does gravitational pull of the moon cause?
Answer:
1).