长难句分析与阅读理解策略 — 英语填空题
题目
阅读句子：Although the archive had been closed for months, researchers, who had assumed that every surviving map was drawn after the flood, found that several maps, which had been stored in a dry room, were copies of earlier originals. 根据句子结构，研究者原先认为每一幅留存下来的地图都是 ___。