What are the 3 most valuable companies in the world?

I'm curious, could you please elaborate on the current ranking of the three most valuable companies in the world? Are they all from the technology sector, or do other industries like finance or retail make an appearance as well? Furthermore, how have their valuations changed over the past year, and what factors have contributed to their position at the top of the list? Lastly, are there any emerging companies that could potentially challenge their dominance in the future?