当需要打开A盘上的abc.txt 文件用于输入时，则定义文件流对象的语句为______ 。

A．fstream fin(“A: abtxt”)；

B．ofstream fin (“A: abtxt”)；

C．ifstream fin(“A: abtxt”,ios:: ap；

D．ifstream fin(“A: abtxt”,ios:: nocreat；

Rapid advances in computer and communication technologies have resulted in the (71) merger of these two fields. The lines have bluned among computing, switching, and digital transmission equipment, and the same digital techniques are being used for data, voice, and image transmission. Merging and evolving technologies, coupled with increasing demands for efficient and timely collection, processing, and (72) of information, are leading to the development of (73) that transmit and process all types of data. The ultimate goal of this evolution is something its proponents-some of the most powerful forces in the computing and telecommunications industries-call the (74) .The (74) will be a worldwide public telecommunications network that will deliver a wide variety of services. The (74) will be defined by the standardization of user interfaces, and will be implemented as a set of digital switches and paths supporting a broad range of traffic types and providing (75) processing services. Inpractice, there will be multiple networks, implemented within national boundaries, but from the user’s point of view there will be a single, uniformly accessible worldwide network.

A．specific
B．dissemination
C．protocols
D．communication