[求助]prep 171

171. Even though it was not illegal for the bank to share its customers' personal and financial information with an outside marketing company in return for a commission on sales, the state's attorney general accused the bank of engaging in deceptive business practices by failing to honor its promise to its customers to keep records private.

A. by failing to honor its promise to its customers to keep

B. by its failure of honoring its promise to its customers to keep

C. in its failing to honor its promise to its customers of keeping

D. because of its failure in honoring its promise to its customers in keeping

E. because of its failure to honor its promise to its customers of keeping

answer:A; 

不明白？    by doing sth的施动者不是句子主语“the state's attorney general ”， 但这样逻辑上又不对了啊？？！！

请帮忙指点一下！谢谢了

这边的by doing 用于说明 engaging in deceptive business practices 的方法

对于B而言 A 的 to do 要优于B 的of doing