[单项选择]The economy in the United States is heavily dependent on aluminum, a material widely used in the construction of buildings and in making such diverse things as cars, airplanes, and food containers. In 1979 Americans used over five million tons of new aluminum, and one and a half million tons of recycled aluminum. Some ninety percent of the bauxite (矾土) ore from which new aluminum is normally derived had to be imported, to meet the demand. Poorer ores are abundant in the United States, however, and researchers at Purdue University may recently have found a way to obtain aluminum magnetically from these.
Although aluminum is not attracted by ordinary magnets, under special conditions it becomes temporarily "paramagnetic", or very weakly responsive to a magnetic field. This is achieved by immersing ore particles in water to which certain salts have been added and then filtering the ore through steel wool in the presence of a strong magnetic field. It is hoped that this technique will
A. construction and manufacturing industry in the United States
B. new technique of obtaining aluminum from poor ores
C. consumption and production of aluminum in the United States
D. the annual import of high-grade aluminum into the United States