Answer: C
Correct answer: It controls the layout, fonts and colours of every slide based on it
The Slide Master holds the design that every slide inherits - background, fonts, colours, placeholder positions, bullet styles, and any logo or element to appear throughout. Changing it changes every slide at once. That central control is its whole point. Formatting fifty slides by hand gives fifty independent settings that drift apart; editing the master gives one. Beneath the master sit layouts - Title Slide, Title and Content, Two Content, Blank and others - each of which can be customised separately, and each slide uses one of them. A deck may also contain several masters, which is how two visual styles are combined in one file. It is reached from View, then Slide Master, and closed with Close Master View. The Handout Master and Notes Master control the printed forms in the same way. Working through the master rather than slide by slide is the single biggest saving of effort in PowerPoint.