T-9-Q27大全987-606

T-9-Q27.
  大全987-606 C
   A

Research during the past several decades on the
nature of language and the processes that produce and make it understandable
has revealed great complexity instead of underlying simplicity.

A.     
that produce and make it understandable has revealed great
complexity instead of underlying simplicity

B.     
of producing and understanding it have revealed not
underlying simplicity but great complexity

C.     
by which
   it is produced and understood
has revealed not underlying simplicity but great complexity

D.     
by which
it is produced and understood have revealed great complexity rather than
underlying simplicity

E.      
by which
one produces and understands it have revealed great complexity instead of
underlying simplicity

606,
sec19-07

A我认为应该是省了it，make
it understandable这种表达可以理解为make understandable it，make可以接宾语+宾补，produce不能加宾补，所以produce可以与make共用宾语it，但不可以共用宾补, produces可以省略it。

C,  it 不能understood,
  应该理解为it was understood by the processes ，这样句意改变不合逻辑。

问题：

我感觉 C选项中it可以指代the nature of language, 这样就可以被understood 的了 

请教大牛

论坛里搜吧，nn的讨论2小时看不完

就是因为这题没有讨论链接才发帖的啊