Populus Euphratica(胡杨) is the only tree species    1     (find)in the desert of North China. In Ejina(额济纳)in the west of Inner Mongolia, there's a Populus Euphratica. As the     2     (old) tree in this Populus Euphratica forest, it    3     (guard) this place for more than 800 years. The locals call it the "sacred tree". Dinosaurs     4     (die) out about 65 million years ago. Then a new species appeared along the ancient Mediterranean Sea. That's the Populus Euphratica. Seasonally flooded river beds(河床) in the Gobi desert are perfect for the Populus Euphratica.     5     there is water, the Populus Euphratica grows.

Populus Euphratica loves water,     6     it also highly resistant to drought. As long as the groundwater is at least 4 meters below, Populus Euphratica can live    7     ( comfortable). If the groundwater level drops below 9 meters, it will die.

Because the course of desert rivers changes frequently, Populus Euphratica has left its mark across the desert. It acts as a good windbreak, prevents sand erosion, and is salt resistant.     8     adult Populus Euphratica can discharge tens of kilograms of salt and alkali(碱) every year. When the wind is blocked, the sand is fixed, and the soil is improved. So the ecological environment of Ejina is protected.

To the south of the Populus Euphratica forest in Ejina, lies Badain Jaran, the third largest desert in China.     9     this 260 square kilometer Populus Euphratica forest, the Badain Jaran Desert, already 49,200 square kilometers in size, would spread northward,     10     (squeeze) the living space of humans. These Populus Euphratica trees form a golden natural barrier, guarding the ecology of Ejina year after year, for another 800 years.