_________ computers are used in Banking, Railways, and Airlines.

Answer: Option D

Mainframe computers are computers used primarily by large organizations for critical applications; bulk data processing, such as census, industry and consumer statistics, enterprise resource planning; and transaction processing. They are larger and have more processing power than some other classes of computers: minicomputers, servers, workstations, and personal computers.

Mainframes are built to be reliable for transaction processing as it is commonly understood in the business world: the commercial exchange of goods, services, or money. A typical transaction, as defined by the Transaction Processing Performance Council, updates a database system for inventory control (goods), airline reservations (services), Railway or banking (money) by adding a record.

Source : wikipedia.org