In this task, you are given a question and an answer, you would be asked to create the sentence based on the Question-Answer provided. It should be contained within the Question-Answer provided.

Question: Which observation demonstrates that light waves travel much faster than sound waves? Answer: An exploding firework is seen before it is heard.
An exploding firework is seen before it is heard observation demonstrates that light waves travel much faster than sound waves.

Question: With what does an electromagnetic wave start? Answer: vibrating charged particle
With vibrating charged particle does an electromagnetic wave start.

Question: What is less dense then either solids or liquids? Answer: gases

Gases is less dense then either solids or liquids.