若磁盘上已存在某个文本文件，其全路径文件名为d:\shiti\tes.txt，下列语句中不能打开该文件的是( )。

A．ifstream file("d:\shiti\testxt");

B．ifstream file("d:\\shiti\\testxt");

C．ifstream file;filopen("d:\\shiti\\testxt");

D．ifstream* pFile = new ifstream("d:\\shiti\\testxt");

Both bus and tree topologies are characterized by the use of multipoint (16) ．For the bus，all stations attach，through appropriate hardware (17) 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 (18) ．A transmission from any station propagates the length of the medium in both directions and can be received by all other (19) ．At each end of the bus is a (20) ，which absorbs any signal，removing it from the bus．

A．routers

B．stations

C．servers

D．switches