A B C 如何区别

斯巴达

T-9-Q27. 大全987-606
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

weirui5621

B：have错，主语是research改成has
AC比较，主动优于被动
我觉得C还有一个问题在于which。这个which究竟是指the nature of language and the processes 还是只指the processes