阅读理解的一问

The tower of Big Ben, London’s most famous building, has always leaned (倾斜) slightly, but construction work on a new line for the London Underground seemed likely to give the tower a real lean. Engineers have had to prop up (支撑) its base to prevent it from damaging the rest of the Houses of Parliament. To control the tower’s movement, engineers pumped grout (水泥浆) into the soil under the tower. The tower now leans an extra few centimeters, but the lean can only be seen by the most sharp-eyed observer. Between 1995 and 1997, to lengthen the Jobilee line of the Underground, builders dug a 40-metre-deep hole just 31 metres north of the clock tower. And the new tube (underground) tunnels were even nearer to the tower. John Burland, who recently helped stop the increasing lean in the Leaning Tower of Pisa and was an adviser to the Jubilee line project, believed the work would affect the tower. In his opinion, no further lean should go beyond a safety limit of 27.5 millimetres over the existing lean of 220 millimetres. To keep the lean within this limit, Burland told the British Association about the new method of pumping grout immediately under the base of the tower. More than 300 tons of grout were pumped in during construction. The tower’s additional lean went between 10 and 25 millimetres, but never passed 27.5 millimetres. After the construction work was completed in late 1997, a review of movements in nearby walls showed that the building was in better shape than had been thought before and the safety limit was raised to 35 millimetres before any action needs to be taken. Since 1997, the tower has continued to lean, Burland told Modern Construction. The latest measurements, taken this year, suggest that the tower’s lean had just reached 35 millimetres. But following regular re-examinations of the tower, experts are sure that the tower has stabilised (稳定). A spokesman for London Underground says: “We understand the tower has stabilized and returned to its normal movement cycle.” From Modern Construction, 16 September 2000 rrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr 69. What was the existing lean of the tower at the time when the article was written? A. 220 millimetres. B. 255 millimetres. C. 35 millimetres. D. 27.5 millimetres.

解题思路： the building was in better shape than had been thought before and the safety limit was raised to 35 millimetres before any action needs to be taken. ……这座建筑物要比先前预料的状况好；而且在采取措施之前的安全限度增加到了35毫米。
解题过程：
正确答案是B。
从文中第三段可知，1995年至1997间，钟塔的倾斜度已达220毫米；而最后一段提及，塔新增的倾斜度是35毫米。因此钟塔目前的倾斜度应是255毫米。
最终答案：略