题目解析:
题干问威尼斯需要进口盐的两个理由?信息定位到本段最后两句话,But Chioggia produced a fine-grained salt, so when Venetians wanted coarser salt, they had to import it. Then, in the thirteenth century, after a series of floods and storms destroyed about a third of the salt-producing ponds in Chioggia, the Venetians were forced to import even more salt. Chioggia 只生产细盐 fine-grained salt,所以威尼斯人所需的粗盐 coarser salt 就需要进口;而且,在十三世纪,由于一系列的洪水暴风雨破坏了 Chioggia 这个地方的盐池,所以威尼斯也必须要进口更多的盐了。故而选项对应为 B(进口可以提供给威尼斯人当地所不能生产的盐,即粗盐)和 C(因为天然灾难破坏了部分产盐地,所以威尼斯需要进口更多的盐)