Why did president obama get two terms?

a.) people wanted him to be president again.
b.) he ran for president a second time and won.
c.) because every black man gets a longer sentence.

Hmm.. I find the third option kind of like an uncomfortable option (I am not sure if other's feel the same way). 

But to answer the question, presidents (among other types of elected officials) can run for two terms. In order to win the second term (which is after 4 years in office), the president needs to run again and if the public (citizens) want that president again as opposed to his opponent (which is usually of a different party, such as Mitt Romney in 2012), then that president can be the president for two terms. So Choice B  seems to be the more valid choice.