It can be inferred from the passage that a historian who wished to compare crime rates per thousand in a European city in one decade of the fifteenth century with crime rates in another decade of that century would probably be most aided by better information about which of the following?
從文章中可以推斷出來，一個(gè)希望比較十五世紀(jì)以前一個(gè)十年的某個(gè)歐洲城市中的每千人的犯罪率與另外一個(gè)十年中的犯罪率的歷史學(xué)家將會(huì)被以下那種信息的提高所的幫助?