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 reduce the amount of high-grade aluminum the United States must import.
The passage focuses on ______.

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