题目内容：
根据以下资料，回答题： Man has been storing up useful knowledge about himself and the universe at the rate which has been spiraling upward for l0,，000 years．
The 21 took a sharp upward leap with the invention of writing，but even 22 it remained painfully slow for several centuries．The next great leap forward 23 knowledge acquisition did not occur 24 me．invention 6f movable type in the l5th century by Gutenberg and others． 25 to 1500，by the most optimistic 26 Europe was producing books at a rate of 1000 titles per year．This means that it 27 a full century to produce a library of l00，000 rifles．By l950，four and a half 28 later，the rate had accelerated so sharply that Europe was producing 120，000 titles a year． 29 0nce took a century now took only ten months．By l960，a 30 decade later，the rate had made another significant jump， 31 a century’s work could be finished in seven and a half months．32 ，by the midsixties，the output of books on a world 33 ，Europe included，approached the prodigious figure of 900 titles per day．
One can 34 argue that every book is a net gain for the advancement of knowledge．Nevertheless we find that the accelerative 35 in book publication does，in fact，crudely 36 the rate at which man discovered new knowledge．。For example，prior to Gutenberg 37 11 chemical elements were known．Antimony，the l2th，was discovered 38 about the time he was working on his invention．It was fully 200 years since the llth，arsenic，had been discovered．39 the same rate of discovery continued，we would by now have added only two or three additional elements to the periodic table since Gutenber9．40，in the 450 years after his time，cer tain people discovered some seventy additional elements．And since l900 we have been isolating the remaining elements not at a rate of one every two centuries，but of one every three years．
A．accumulation
B．development
C．knowledge
D．rate
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答案解析：