同步拓展阅读：新概念英语第3册第2课
一、往期回顾
【参考答案】
1. The isolating effects of human development.
2. There is far less interbreeding among populations.
3. Lower genetic diversity.
4. Four to six.
5. They will lose their resilience.
二、本期内容
【课文主题】
第2课的主题是钟塔（clock towers），所以我选择了一篇同样是有关楼塔的文章。
【拓展阅读】
一、文章内容
Why has the Leaning Tower of Pisa survived the strong earthquakes that have hit the region since the middle ages? This is a long-standing question a research group of 16 engineers has investigated, including a leading expert in earthquake engineering and soil-structure interaction from the University of Bristol.
Professor George Mylonakis, from Bristol's Department of Civil Engineering, was invited to join a 16-member research team, led by Professor Camillo Nuti at Roma Tre University, to explore this Leaning Tower of Pisa mystery that has puzzled engineers for many years.
Despite leaning precariously at a five-degree angle, leading to an offset at the top of over five metres, the 58-metre tall Tower has managed to survive, undamaged, at least four strong earthquakes that have hit the region since 1280.
Given the vulnerability of the structure, which barely manages to stand vertically, it was expected to sustain serious damage or even collapse because of moderate seismic activity. Surprisingly this hasn't happened and until now this has mystified engineers for a long time. After studying available seismological, geotechnical and structural information, the research team concluded that the survival of the Tower can be attributed to a phenomenon known as dynamic soil-structure interaction (DSSI).
The considerable height and stiffness of the Tower combined with the softness of the foundation soil, causes the vibrational characteristics of the structure to be modified substantially, in such a way that the Tower does not resonate with earthquake ground motion. This has been the key to its survival. The unique combination of these characteristics gives the Tower of Pisa the world record in DSSI effects.
二、阅读题目
根据文章内容回答下列问题：
20. What did the 16-member research team try to explore?
21. How many earthquakes have hit the Tower so far?
22. What was expected to happen to the Tower if there was a moderate seismic activity?
23. According to the research team, what phenomenon secures the survival of the Tower in earthquakes?
24. What is the key to the survival of the Tower in earthquakes?