Requiring the vaccination of schoolchildren, even if their religion opposes it
George Washington was the first president.
The answer to the question presented above would be letter b. amount of dissolved gases. The increased pressure increases the body's amount of dissolved gases. This change to air pressure greatly affects the human body and these changes can happen when going into the depths of the ocean or when climbing mountain peaks.
If I'm not mistaken, it was used as a neutral zone. Basically splitting hostiles from non-hostiles. It was also being used as a safe haven for the poor who couldn't pay taxes.
I hope this is the answer you were looking for and that it helps!! :)