Please help me, I’m confused

Which sentence states the main idea of the paragraph?

A.) The topic sentence, which indicates that Coit Tower is both interesting and little known

B.) the topic sentence, which indicates that Coit Tower was built on a hill

C.) the supporting sentence that states that the tower was built as a memorial to Lillie Hitchcock Coit

D.) The supporting sentence that states that many murals were painted on the tower's walls