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

[spoiler]OA: By vs Because???? Which one is better and why????[/spoiler]