An experiment is done to test if the color of a website link affects the likelihood that people will choose to click on it$.$ The result is that a particular shade of blue has the highest click likelihood of any color tested by far. However, it turns out that a software bug caused each participant's computer to display certain colors faintly. In fact, the winning shade of blue was also the only shade that correctly displayed on all participant computers. In the language of experimental design, the most accurate description is that

a$)$ the color of the link and whether the color displayed properly were confounded.

b$)$ the color of the link was the dependent variable and whether the color displayed properly was the independent variable.

C$)$ the color of the link and whether the color displayed properly were both extraneous variables.

d$)$ the color of the link and whether the color displayed properly were both independent variables.