在大型及复杂项目的实施与控制过程中，最关键的环节是(68)。

(71)

(70)

(69)

(68)

IPv6 is short for "Internet Protocol Version 6". IPv6 is the "next generation" protocol designed by the IETF to(71) the current version Internet Protocol, IP version 4("IPv4").

 Most of today's internet uses IPv4, which is now more than twenty years old. IPv4 has been(72) resilient in spite of its age, but it is beginning to have problems. Most importantly, there is a growing(73) of IPv4 addresses, which are needed by all new machines added to the Internet. IPv6 fixes a number of problems in IPv4, such as the(74) number of available IPv4 addresses. It also adds many improvements to IPv4 in areas such as routing and network autoconfiguration. IPv6 is expected to gradually replace IPv4, with the two coexisting for a number of years during a transition(75) .

通常，多项目管理从项目目标卜看，这些项目可能是孤立的、无关联的，但是这些项目之间的组织内部存在除(70)之外的共有特性。

在大型及复杂项目的实施与控制过程中，最关键的环节是(68)。

以下关于大型及复杂项目的计划过程的描述，错误的是(69)。

某项目年生产某种产品250万件，每件销售价为8元，可变单位成本5元，固定成本210万元，则该项目的盈亏平衡点销售额为(66)。

通常，大型及复杂项目的管理模式以间接管理为主。以下关于“间接管理”的描述中，正确的是(67)。