One hallmark of the mortgage-banking crisis, robo-signing, in which banks blindly accepted legal documents without checking them for accuracy or authenticity, has led to a series of lawsuits against large banks such as Bank of America and Citigroup.

A. One hallmark of the mortgage-banking crisis, robo-signing, in which banks
B. Robo-signing was one hallmark of the mortgage-banking crisis, in which banks
C. Robo-signing, which was one hallmark of the mortgage-banking crisis and which banks
D. One hallmark of the mortgage-banking crisis was robo-signing, in which banks
E. One hallmark of the mortgage-banking crisis was robo-signing, and banks