The correct answer is D. pt.
A point (pt) is a unit of measurement used in typography and graphic design. It is equal to 1/72 of an inch. Points are used to measure the size of type, the leading (space between lines of type), and the kerning (space between individual letters).
Pixels (px) are a unit of measurement used in digital images. They are the smallest unit of a digital image, and they are used to represent the color and brightness of each individual point on the screen.
Inches (in) are a unit of measurement used in the imperial and US customary systems of measurement. They are equal to 1/12 of a foot.
Ems (em) are a unit of measurement used in typography. They are equal to the current font size. Ems are often used to measure the size of elements that should be proportional to the font size of the surrounding text.