Most of the sandstorms that had swept China last year originated from foreign land，a Chinese official in charge of desertification control said on Monday.And the invasions(入侵) could partly explain the frequent sandstorms in the country in recent years despite its achievements in desertification control.

　　Since the start of last spring，the north and northwestern Chinese regions had been hit by 17 sandstorms，of which，a dozen came from foreign land.

　　Situated in the central­Asia sandstorm region，one of the world's four largest sandstorm sources，China also suffers from sandstorms from outside the country while being blamed as a sand source to northeast Asia.The other three major sources are in Africa，North America and Australia.

　　The land suffering from desertification has been decreasing by 7,585 sq.km annually in China，and the area of sandy land has also been falling by 1,284 sq.km a year.

　　The shrinkage(收缩) forms a clear contrast to the fact that the land suffering from desertification and sandy feature was added by 10,400 sq.km and 3,436 sq.km late last century，respectively.

　　Currently，the desertification land in China makes up 2.64 million sq.km，accounting for 27.46 percent of the nation's land，and its sandy land totals 1.74 million sq.km，accounting for 18.1 percent of the country's total.

根据短文完成下列各题

1．Where do most of the sandstorms in China come from?

Foreign countries.

2．What does the underlined word "decreasing" mean in Paragraph 4?

It means "going down"．

3．Which is believed to be the sand source to northeast Asia?

China.