The sentence fragment present in those sentences is...
Regina and her younger sisters.
That's true, very inspiring
I believe the answer is that they separate syllables.
I hope this helps.
1. I am an astronaut because I float in space and look at earth 2.I am a princess because my father has a crown and I have to wear a dress 3.I am a baseball player because I swung with a bat and there is a pitcher 4.I am an artist because I have a canvas and brushes 5.I am a mechanic because I sell parts of things to people