根据国际商会《跟单信用证统一惯例》（UCP600）的规定，如果受益人按照信用证的要求完成对指定银行的交单义务，出现下列哪些情形时，开证行应予承付？

A．信用证规定指定银行议付但其未议付

B．信用证规定指定银行延期付款但其未承诺延期付款

C．信用证规定指定银行承兑，指定行承兑但到期不付款

D．信用证规定指定银行即期付款但其未付款

Both bus and tree topologies are characterized by the use of multipoint (1).For the bus, all stations attach, through appropriate hardware (2) known as a tap, directly to a linear transmission medium, or bus. Full-duplex operation between the station and the tap allows data to be transmitted onto the bus and received from the(3). A transmission from any station propagates the length of the medium in both directions and can be received by all other  (4). At each end of the bus is a (5) , which absorbs any signal, removing it from the bus.

空白（2）处应选择（）

A.processing

B.switching

C.routing

D.interfacing