问题补充：
The Great Wall is tourist attraction that millions of people pour in every year.
A. so well-known a
B. a so well-known
C. such well-known a
D. a such well-known
答案：
(答案→)A. so well-known a
B. a so well-known
C. such well-known a
D. a such well-known
解析：so…that用于以下四个句型：
so+形容词/副词+that…
so+形容词+a/an+单数可数名词+that…根据这一条故选A。
so+ many(多) / few(少) +复数可数名词+that…
so+ much(多) /little(少) +不可数名词+that…
such…that作“如此?以致”解，连接一个表示结果的状语从句。与so?that意思相同，但用法不同。如：so?that这一结构中，so后边可加形容词或副词，而such后边要用名词（这个名词前面可以带形容词，也可以不带）。因此，such…that的句型结构可分以下三种：
such＋a(an)＋adj.＋单数可数名词＋that?clause
He is such a clever boy that everybody likes him.他非常聪明，大家都非常喜欢他。
such＋adj.＋复数可数名词＋that… They are such interesting novels that I want to read them once again.这些小说非常有趣，我想再读一遍。
such＋adj.＋不可数名词＋that?clause He has made such great progress that the teachers are pleased with him.他进步得很快，老师们对他感到很满意。
注意：如果such后边的名词前由many、much、few、little等词所修饰的话，则不用 such而用so。例如： He had so many falls that he was black and blue all over.他摔了很多跤，以致于全身上下青一块，紫一块的。 He had so little education that he was unfit for this job.他所受教育很少，不适合做这个工作。 There were so many people in the street watching the fire that firefighters could not get close to
