填塞塑料最佳的时期是A．粥状期B．丝状期C．橡皮期D．硬化期E．以上都不是

第二节：（共5小题；每小题2分，满分10分）

根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

       71  It is a new term in today's tourism industry．But in an age of growing environmental awareness, it is not too difficult for us to imagine and understand this new form of holiday．

Ecotourism, which is considered as a kind of responsible tourism, is typically defined（定义）as travel to places where special and unusual plants, animals and cultural heritages （遗产） are the main attractions．  72  Therefore, programs concerning the protection of some natural and cultural spots also form'a part of ecotourism．

Ecotourism is developing at great speed．According to a recent report by the World Tourism Organization, ecotourism in recent years has enjoyed an annual growth of about 5% worldwide．  73  They include bird watching, hiking, diving, photography and taking part in various kinds of local cultural events．

        74  However, it looks like some smaller towns and country areas may well become the new destinations for people to visit tomorrow because they are rich in ecological, cultural and historical resources （资源）．

Ecotourism has been gaining increasing recognition and popularity mainly for the relaxing, natural and vivid experience it offers to tourists．People are attracted to nature  and long to be close to it．However, a conflict between nature and human beings is unavoidable．  75 

A．The definition of ecotourism is beyond words．

B．It takes ecology and culture into consideration．

C．You may not be very familiar with "ecotourism"．

D．More than 80 activities have been listed for ecotourism． E．People can have great fun enjoying nature through ecotourism．

F．Big cities are still the major places ．that attract tourists in our society today．

G．How to protect natural resources while taking advantage of them is of great importance．

简述建构主义学习理论的基本观点。

每节钢轨有（）不同的轨枕间距。

A、2种

B、3种

C、4种

D、5种

在TCP/IP网络的传输层有两种传输协议，其中TCP是一个面向连接的协议，它提供 (253) 的连接功能，采用 (254) 技术来实现可靠数据流的传送。为了提高效率，又引入了滑动窗口协议，协议规定重传 (255) 的分组，这种分组的数量最多可以 (256) ，TCP协议采用滑动窗口协议解决了 (257) 。

（254）处填（）

A.超时重传

B.肯定确认（捎带一个分组的序号）

C.超时重传和肯定确认（捎带一个分组的序号）

D.丢失重传和重复确认