Definition: In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.
Input: Passage: Twenty Palaeolithic sites have been identified in the Mendips, of which eleven represent faunal remains and lithic artefacts recovered from caves. The remaining eight sites refer to surface lithic discoveries, and the artefacts found include points, scrapers, and handaxes. Twenty-seven Mesolithic finds are represented by flint and chert lithics. Large numbers of artefacts have been found near Neolithic, Iron Age, and Bronze Age features, such as the barrows and forts around Priddy and at Dolebury Warren. The caves of Cheddar Gorge have yielded many archaeological remains, as flood waters have washed artefacts and bones into the caves and preserved them in silt. The Cheddar Man, Britain's oldest complete skeleton, was found in Gough's Cave, part of the Cheddar Complex.Within the Mendip Hills AONB, good evidence exists for 286 definite examples of round barrows, including the Priddy Nine Barrows and Ashen Hill Barrow Cemeteries. The Historic England Archive holds over 1,200 entries for the area, and there are over 600 listed buildings, in addition to over 200 scheduled ancient monuments. These protected monuments range from prehistoric barrows and hillforts to the Black Down bombing decoy from the Second World War.Settlement on the Mendip Hills appears to fall into two types. The first, apparent in the Neolithic and Bronze Age Britain periods, and repeated on a small scale in the Middle Ages and post-medieval era, comprised occupation by self-sufficient groups in small communities or isolated farms. The second was represented in the Iron Age Britain and Roman periods by large sites with specialist functions, existing by virtue of their ability to exert power over lowland producers. From the Iron Age onward the ownership of land took on increasing importance, with large landholdings based on the mines or on stock grazing, denying settlers access to the plateau or forcing them off the hills.There is evidence of mining dating back to the late Bronze Age, when there were technological changes in metal-working indicating the use of lead. The Roman invasion, and possibly the preceding period of involvement in the internal affairs of the south of England, was inspired, in part, by the mineral wealth of the Mendips. Much of the attraction of the lead mines may have been the potential for the extraction of silver;
the Latin "EX ARG VEB" stamps on the Mendip lead pigs specify a de-silvering process and cast silver ingots have been found. The silver coinage of the Dobunni and Durotriges is also likely to reflect the availability of silver from the mines.
Output:
What culture's invasion of the hills that were occupied by two types of settlements was most likely for silver?