将以下三句按照正确的顺序排列,使其符合引言开头的论证逻辑。a.In recent years, there has been an increased awareness of the potential impact of pollutants such as heavy metals. b.Moreover, the traditional methods for treating aqueous streams containing metal contaminants are expensive and can have inadequate facilities. c.The use of biological materials is one such technology which has received considerable attention. d.This has led to the use of alternative technologies.