The tower of Pisa is the bell tower of the cathedral of Pisa in Tuscany, Italy. It leans because when the building was half completed, the soil under one half of the circular structure began to subside and the tower tipped. Work on the tower was begun in 1173, but was discontinued for a century after the subsidence. However, in 1275, architects devised a plan to compensate for the tilt. Two stories, the third and the fifth, were built out of line with the others and closer to the vertical in an effort to alter the tower’s center of gravity. But the leaning has continued to increase gradually throughout the centuries. Pumping to keep water away from the surrounding ground and the injection of cement grout into the foundations and the surrounding subsoil have been tried in recent years, but without success. The tower, which is one of the most unusual in existence, is Romanesque in style and made of white marble. It is cylindrical in shape and has eight stories. The tilt is about 17 feet, or more than five degrees, from the perpendicular. The tower continues to increase its tilt by about a quarter of an inch each year.
46 What is the main idea of this passage?
(A)Of all the tourist attractions in Italy, the tower of Pisa is undoubtedly the most popular.
(B)The collaboration of the Italian government and people has made the tower of Pisa become famous.
(C)The best way to study Italian culture is to visit the tower of Pisa.
(D)espite the effort over the past years, the tower of Pisa still keeps tipping.