A、The development of French engineering firms. B、Working and living condition in the city of Dijon. C、The environmentally-friend

　　(3) A French engineering firm has built what is being hailed as the world’s most environmentally sound building, a structure that produces more energy than it consumes. The ten-story building is located in Dijon, and it is part of a concerted effort to put the city on a sustainable energy path.
　　The Elithis tower is a striking sight in the heart of Dijon’s business district. Black, with a red metal skirt—which actually is a sun shield—it is sandwiched between the city’s opera house and a hotel. But the tower is more than just another handsome landmark—from the ground floor to (4) its solar paneled roof, it is an experiment in a greener way of working and living.
　　Francois Pocheron, a senior manager for the Elithis engineering firm that designed the tower, takes visitors on a tour of the building. Just about every aspect of its design and construction is aimed at conserving energy and using natural elements like sunlight and rain.
　　3.  What is this news report mainly about?
　　4.  What is the roof of the Elithis tower made of?