贸易保护是把“双刃剑”。一个国家在运用技术性贸易壁垒阻碍外国农产品进入本国市场，给出口国生产企业造成损失的同时，也给本国的经 销商和消费者带来相应的伤害。这种做法未必会得到国内不同人群的一致支持。这种情况实际也为出口企业提供了一种可能，即可以由行业协会出面，通过联合进口 国的民间组织，向他们的政府施加影响，促其作出让步，解除贸易保护。适合本段文字的小标题是：

A．贸易保护是把双刃剑

B．发挥行业协会作用，解除进口国的贸易保护

C．贸易保护的利弊

D．贸易保护的作用

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) .

A．days

B．period

C．phase

D．epoch