从题中所给的A、B、C、D 四个选项中选出能填入空白处的最佳选项。

The world is divided into two main parts, the poor and the 1. The poor countries 2"the developing countries", which have special 3. Sometimes the land is too poor to grow anything

4. Many people never get enough food 5, and the children starve（饿死）. Help should be given by the rich countries, but rich countries have problems, 6. The air isn't fresh and the rivers are7 dirty to swim in or8 water from. Also the roads are too9 to drive along. And sometimes, large numbers of people 10 not have pleasant houses to live in. So something will have to be done about the problems.