试分析沼气发酵在国民经济和环境保护中的重大战略意义。

B Egyptian Villages 埃及村落

Most of the inhabitants live in mud-brick homes, their (1)  walls insulating against the afternoon heat. Flat roofs, exposed (2)  the northern evening breezes, serve as cool sleeping (3)  as well as storage areas. Villagers plaster the outer walls (4)  often trim them in blue, a color they believe (5)  off the evil eye. As a man becomes richer, (6)  can add a second story to his house perhaps (7)  his married son. Those villagers who have made the (8)  to Mecca paint the legend of their trip on (9)  outer walls of their homes. Such hajj houses, along (10)  the mosques, are the most distinguished buildings in a (11)

Some villagers build ornate pigeon coops close to their (12) , using the birds as food and their droppings to (13)  crops. Many houses still have dirt floors and lack (14)  or running water; women with jars balanced on their (15)  make the trek to the community well, and children donkeys haul the (16)  liquid in jerry cans.

All (17)  said, government sponsored building programs have also brought newer (18)  residences and utilities to some villages, particularly those outside (19)  Nile Valley in the Oases and the Red Sea (20)  areas.

20.（）