which of the following financial institutions was originally known as a Building Society?

The financial institution that was originally known as a Building Society is the Mortgage Bank. A Building Society is a type of financial institution that provides loans to individuals for buying or building houses. It raises funds by accepting deposits from its members, which it then uses to provide mortgage loans at low-interest rates. As the name suggests, a Mortgage Bank is a financial institution that specializes in providing mortgage loans to individuals and businesses. It raises funds by issuing bonds, accepting deposits, and borrowing from other financial institutions. Therefore, the correct option is "Mortgage banks."