Merlia is creating a presentation about her ethnic heritage for a homework assignment. her friend john, a powerpoint 2016 expert, is her add transitions. john tells merlia that it is often best to use the same slide transition consistently. he shows her the button which applies the transition to all the slides in the presentation.

"apply to All"

Explanation:

The “Apply to All” button repeats a slide customization across all your slides, leaving them evenly. With this button, a modification made to one slide can be applied to all slides. This makes the power point presentation even and visually pleasing.

Since John told Merlia that it's often better to use the same slide transition consistently, we can conclude that John showed Merlia the "apply to all" button so she can apply the same transition to all slides in the presentation.