Problem: What are the most important words?
volcanic activity under meromictic lake produced a cloud of carbon dioxide that asphyxiated villagers
Answer: activity, asphyxiate, dioxide, lake, produce

Problem: What are the most important words?
mountaineers descending a high alpine mountain to the waiting clouds and valley below
Answer: cloud, descend, valley

Problem: What are the most important words?
dangerously steep stairs lead to the towers of the inner court
Answer:
lead, stair, tower