Look up any of his books and check out his word play
Most schools ban soft drinks from student vending machines. It happened when Obama was President & his wife Michelle Obama decided to get rid of all unhealthy food & drinks at schools. Most schools today still observe a healthy diet in schools today.
C - The Leaning Tower of Pisa, which started construction in 1173, did not begin sinking into the ground until the third story was built.
The use of commas sets off the dependent clause (which started construction in 1173).