GRE Text Completion: Princeton-GRE填空Princeton - C93CC64C3TCLZ06Q9

Since a large number of the ores frequently located in riverbeds are (i)____________ on the earth's surface, where the processing of chemicals is less costly, recovery of underwater ores is not likely to become a (ii)____________ procedure. A. scanty B. valuable C. abundant D. cost-effective E. preserved F. rejected