CR Question, could you please help me?/LSAT-7-1-1

Before the printing press, books could be purchased only in expensive manuscript copies. The printing press produced books that were significantly less expensive than the manuscript editions. The public’s demand for printed books in first year after the invention of the printing press was many times greater than demand had been for manuscript copies. This increase demonstrates that there was a dramatic jump in number of people who learned how to read in the years after publishers first started producing books on the printing press.

Which one of the following statement, if true, casts doubt on the argument?

C. In the first year after the printing press was invented, printed books were purchased primarily by people who had always bought expensive manuscripts but could afford a greater number of printed books for the same money.

D. Books that were printed on the printing press in the first years after its invention often circulated among friends in informal reading clubs or libraries.

答案是D，可是我的理解D是support，因为文中说书的需求量大了，说明学习阅读的人多了，D又进一步说同一本书看的人也多了，说明书的读者是大于购书者的，能阅读的人应该更多呀。C正是说明书的需求量大了，因为原来那些读者买的多了，并不是阅读的人增加了，这才是削弱。是答案错了，还是我的理解有误呀