[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? )

a. it is a compound sentence.
b. it is a compound-complex sentence.
c. it is a simple sentence.
d. it is a dependent sentence.