b. Font Style

In metal typesetting, a font was a particular size, weight and style of a typeface. Each font was a matched set of type, one piece for each glyph, and a typeface consisting of a range of fonts that shared an overall design

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Answer:

It changes the shape of the selected text.

a. Font

b. Font Style

c. Font color

d. Text effects

I'm not sure if Font or Font style but i decided that it's font style and hope it helps.