单选题 从下面的答案中，选出应填入下面叙述中______内的最确切的解答。
   Network managers have long (1) practical voice-over-IP (VOIP) solutions. VOIP (2) ease network management and decreases costs by converging a company's telephony and data infrastructures into one network. And a VOIP solution implemented at a company's head-quarters with far-reaching branch offices can (3) tremendous amounts of (4) in long distance phone bills, provided that solution delivers POTS-Iike voice (5) over the Internet.