In double checking her finished PowerPoint slides, Clara realized that she violated one of the rules for effective presentations. Which of the following should she change?

a$.$ Her title slide has $36pt.$ Text.

b$.$ She has used more than four colors per slide.

c$.$ She has used two font styles throughout: one font for the title and subtitles and one font for other text.

d$.$ She has used phrases instead of complete sentences