Problem: What are the most important words?
a prism splitting white light into a rainbow .
Answer: light, prism, rainbow

Problem: What are the most important words?
working tug boat guiding a large container ship through the narrow entrance of harbour
Answer: boat, entrance, harbour, ship, work

Problem: What are the most important words?
goalkeeper dives to stop the ball during a match as part of fifth round of person .
Answer:
ball, dive, match, stop