B. Millions of Jews were executed by the Nazis
The answer is Radon. Radon is an odorless, colorless and tasteless gas. It is the heaviest among the noble gases. It is, in fact, radioactive. Radon is considered to be a health hazard. It is so radioactive that further studies become very difficult. When radon decays, radon progeny is produced. These new substances stick to the surfaces of dust particles in air. When inhaled may stick to the lung and airway walls.
There would be a scarce amount of food so organisms will start dying out. Food webs would get messed up.
