PREP语法笔记相似题目一点不解

ran2010zx

In addition to being China’sfirst administrators, in the sense that they developed a coherent bureaucracyfor their empire, the first literate culture in East Asia were the Shang,and they were well known for crafting ornate bronze ritual vessels.
A.              the first literate culture inEast Asia were the Shang, and they were well known for crafting
B.              the first literate culture inEast Asia were the Shang, well known as the crafters of
C.              the Shang, as the first literateculture in East Asia, is well known for its crafting
D.             the Shang were the firstliterate culture in East Asia and are well known as the crafters of
E.              the Shang were the firstliterate culture in East Asia and well known
 key: D  
这个题目在PP2008笔记的22页
虽然讨论点不在我想说的地方。。。
我想问下这里的D用的是were还有are
为毛？
商超不是一个朝代么。。。为啥要用复数。。。 如果是从前面的同位结构的THEY来看出的话也不对啊
因为PP语法笔记里面说的很清楚：同位结构中名词的数可以与被同位的不同。。。
不明白， 求解释
谢谢！

ran2010zx

自己顶。。。为啥就没人回答。。。