什么意思？

小嘴金鱼

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
A是正确答案， 什么意思？

小嘴金鱼

C为什么不对呢？

tjbian78

语言的本质以及产生语言并使之能够被理解的过程。。。。