Sydney is Australia’s most exciting city, the history of Australia begins here. In 1788, Captain Apthur Phillips arrived in Sydney with 11 ships and 1624 passengers from Britain (including 770 prisoners). Today there are about 4 million people in Sydney. It’s the biggest city in Australia, the busiest port in the South Pacific and one of the most beautiful cities in the world. There are over twenty excellent beaches close to Sydney and its warm summer climate and cool winter have made it a favorite city for immigrants from overseas. There are three things that makes Sydney famous: its beautiful harbor, the Sydney Harbor Bridge, which was built in 1932 and the Sydney Opera House, which was opened in 1973. 

What does the word “which” in line 8 refer to?