_______ houses were knocked down in the earthquake.    
 A. A great many of　  B. The number of 　 C. A great many　 D. A large amount of  
此题选C。

a great 是用来加强 many 程度的。实际就是 many 和 many of 的区别。

区别：前者 many 是限定词，接复数可数名词，不特指；后者 many 是代词，of 介词短语作 many 的定语。
特别提醒：many of 后面接复数名词和代词，而且名词必须特指，即：名词前必须加 the, these, his 等词语限定。
【比较】
限定词：many books
代词：many of the/these/his books，many of us/them 等。

错误的表达：many of books；many us/them （误）

举一反三，以此类推：
限定词：some books
代词：some of the/these/his books；some of us/them