Read the summary of the conclusion of “The World on Turtle’s Back.”

[1] When the twins grew up, they continued to fight. [2] One day they decided to hold a contest to determine who was stronger. [3] Though they tried to defeat each other in many different ways, neither one could win. [4] On the last day, they fought with weapons. [5] Using a deer antler, the right-handed twin overpowered his brother, and he threw him off the edge of the Earth. [6] Today, the right-handed twin lives in the Sky-World, and the left-handed twin lives in the dark underworld. [7] They rule the earthly world of men together.

Which best describes sentence 7?
It is a compound sentence.
It is a compound-complex sentence.
It is a simple sentence.
It is a dependent sentence.