Final answer:
The primary color formed from adding red is red itself, as red is a fundamental color in art and color theory and cannot be produced by mixing other colors.
Step-by-step explanation:
The primary color formed from adding red is red itself. In the context of art and color theory, primary colors include red, blue, and yellow. These colors are considered fundamental because they cannot be created by mixing other colors and all other colors are derived from a combination of these three. According to the information provided, if you add red to a combination of colors or to red itself, the primary color you are dealing with remains red. Thus, the answer to the question is: a. Red.