BBC news 2010-11-13 加文本

1.But today's intervention has not altered the basic economic fact that Ireland is struggling while figures show the core of Europe is still growing well, with Germany's economy expanding at 0.7%, still the powerhouse of Europe.

这句话的主干是：But today's intervention has not altered the basic economic fact。后面是that引导的同位语从句，指代的是fact。

同位语从句与定语从句的不同之处：

1)从句的作用不同：同位语从句用来进一步说明前面名词的内容；定语从句用来修饰、限定前面的名词。
e.g. The news that our team has won the final match is encouraging. （从句说明“消息”的内容：我们队取得了决赛胜利。）
　　 The news that you told us is really encouraging.（从句对“消息”加以限定：是你告诉我们的，而非来自其他渠道。但消息是何内容却不得而知。）

2)that引导同位语从句时是一个纯连词，故不能用which替换；而that引导定于从句时是代词，常可以和另一关系代词which替换。
e.g. The fact that he is from Canada is new to me. （that不可换为which）

　　 The fact that surprised me is that he is not Chinese.（第一个that可换为which，第二个不行，因为它引导的是表语从句。）

3)引导同位语从句关连词，除that外，还可以根据句义使用任何其它疑问代词或副词；而定语从句不可用what, how, whether等引导。

2.Six thousand performers took part in an unusual inauguration ceremony along the Pearl River, arriving in 45 boats, the number of countries taking part in the competitions.

这句话的主干是前面半句。arriving是现在分词作伴随状语。the number是45的同位语，对前面作进一步的补充说明。