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根据以下资料，回答题。
Giant Structures
It is an impossible task to select the most amazing wonders of the modem world 51 every year more wonderful constructions appear. Here are three giant structures which are worthy of our admiration 52 they may have been surpassed by some more recent wonders.
The Petronas Twin Towers
The Petronas Towers were the tallest buildings in the world when they were 53 in 1999. With a height of 452 metres, the tall twin towers, like two thin pencils, dominate the city of Kuala Lumpur. At the 41st floor, the towers are 54 by a bridge, symbolizing a gateway to the city. The American architect Cesar Pelli designed the skyscrapers.Constructed of high-strength concrete, the building provides around 1,800 square metres of office space on every floor. And it has a shopping centre and a concert hall 55 the base. Other features of this impressive building 56 double-decker lifts, and glass and steel sunshades. The Millau Bridge The Millau Bridge was opened in 2004 in the Tarn Valley, in southern France. At the 57 it was built, it was the world’s highest bridge, reaching over 340m at the highest point. The bridge is 58 as one of the most amazingly beautiful bridges in the world. It was built to relieve Millau’s congestion 59 . The congestion was then caused by traffic passing from Paris to Barcelona in Spain. The bridge was built to withstand the most extreme seismic and climatic conditions. 60 , it is guaranteed for 120 years! The Itaipu Dam The Itaipu hydroelectric power plant is one of the largest constructions of its kind in the world. It consists of a series of dams across the River Parana, 61 forms a natural border between Brazil and Paraguay. Started in 1975 and taking 16 years to complete, the construction was carried out as a joint project between the two 62 . The dam is well-known for both its electricity output and its size. In 1995 it produced 78% of Paraguay’s and 25% of Brazil’s 63 needs. In its construction, the 64 of iron and steel used was equivalent to over 300 Eiffel Towers. It is a 65 amazing wonder of engineering.
请在第_____处填上正确答案。 A．since
B．before
C．so
D．as to
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