Students are using balloons to describe the expanding universe model. The students blow up several balloons and put them on the floor. Each balloon represents a different galaxy. 
 How should the students move or change the balloons to demonstrate how the universe is expanding?
 a
 All of the balloons should be moved to the center of the floor.
 b
 Each balloon should be deflated so that there is more distance between the surface of each balloon.
 c
 All of the balloons should be moved away from each other so there is more distance between them