Today’s lecture is about the mass (1) of the world’s population. There are two major (2) why people are moving to cities. The first reason is (3) . People are moving to the cities because that’s where they can find (4) and earn money. The second reason for the move to cities has to do with (5) of life issues: comfort and (6) . Cities often offer better (7) . And then for many, city life is just more (8) . An interesting consequence of urbanization is that the average (9) of people in the countryside is increasing, while that of the cities is (10) .
Three key (11) can be identified in our cities. First of all, they’re getting bigger. Most cities are bigger now than ever before. Cities are also changing shape. They’re getting (12) , because land is getting more and more expensive. (13) have become a symbol of modern cities.
Cities are also changing shape in other ways. The (14) Model and the (15) Nuclei Model are probably more typical of the cities we know today. They show the urban (16) that’s occurring in contemporary cities.
The third change is that our cities are breaking up into (17) communities, often by (18) group or (19) level. This often means that people stay within their community and do not come into contact with others from different (20) .

下列不是不孕症时月经前1～2天子宫内膜的组织学形态的是（）

A.腺体分泌不佳

B.间质不发育

C.子宫内膜息肉

D.分泌早期形态

E.结核性子宫内膜炎