Sentence 1: Today was a leap day in a leap year. 
 Sentence 3: He just turned 16, but they celebrated Marks 4th birthday 
 Sentence 4:  They thought it was funny, but a cop heard them celebrate 
 Sentence 5:  They finished eating, and the cop stopped Mark to see his license! 
 Option 1: It was Marks birthday but he stayed home to celebrate with family. 
 Option 2: It was also Marks birthday, so he went out with friends.