GRE部分第57句 The molecular approach to detecting peptide hormones using cDNA probes should also be much faster than the immunological method becauseitcan take years of tedious purifications to isolate peptide hormones and then develop antiserums to them.
下面的解释也说道了 本来作主语的it应该指主句主语 但是此处是比较结构 A should be faster than B because it ...... 此处it也可以指代B