Question

Mary can view the thumbnails of her presentation slides when she is creating the slides. Which element of the program’s interface is she seeing?

Answer 1

the element of program's interface that she is seeing is : Slide panel

This feature can usually be found on the left side of the windows.
For microsoft power point, the slide pane displays available slides in a  slide show presentation

Answer 2

Mary can view the thumbnails of her presentation slides when she is creating the slides. The slide panel is the element of the program’s interface she is seeing.