Which symbol completes the musical equation

Make the correct match. 1. only the collection of the louvre is on display. 2. in addition to being a museum, the louvre has also been a 3. the present palace was built to display 4. after the french revolution, it became a 5. in 1989 i.m. pei designed for a new entrance. 6. pei's design actually has 7. the new entrance was required to handle the growing number of half the royal art collections public museum 673 panels the glass pyramid prison visitors