Problem: What are the most important words?
a cypress tree growing in a lake
Answer: grow, lake, tree

Problem: What are the most important words?
firefighters discuss tactics whilst taking part in a simulated chemical incident
Answer: discuss, firefighter, part, tactic, take

Problem: What are the most important words?
woman lay hand upon a mellow wheat ears on a field before gathering a harvest
Answer:
field, hand, harvest