Today, we know that many sicknesses are caused by germs. We prevent the spread of disease by using disinfectants--substances, such as chlorine bleach--that kill germs. The poisonous smoke used by the Chinese was a type of disinfectant (solution to kill germs).
The correct answer is government. Here in the United States, to fill the purpose of government we have things such as the Navy, Air Force and other military branches.
