The correct answer is A. Slide number.
A handout master contains placeholders for all of the following except the slide number. The slide number is a placeholder that is automatically added to each slide in a presentation. It is located in the lower-right corner of the slide. The other placeholders are the title, footer, and header. The title placeholder is located in the center of the slide. The footer placeholder is located at the bottom of the slide. The header placeholder is located at the top of the slide.
The slide number placeholder is not included in the handout master because it is not necessary for a handout. A handout is a printout of a presentation that is used by audience members to follow along with the presentation. The slide number is not necessary for this purpose because audience members can simply look at the slide that is currently being displayed on the screen.
The other placeholders, however, are necessary for a handout. The title placeholder is used to identify the presentation. The footer placeholder is used to include information such as the date, time, and location of the presentation. The header placeholder is used to include information such as the name of the presenter and the title of the presentation.