Concept:Complementary colours are two colours that, when combined additively, produce white light.
Explanation:In additive colour mixing, light of one colour is mixed with its complementary colour.
The combined effect of the two coloured lights is white light.
Common complementary pairs include red and cyan, green and magenta, and blue and yellow.
Such colour pairs do not share the same wavelength.
They also do not have the same refractive index.
Mixing complementary colours never produces black light, because black is the absence of light.
Thus, the defining property of complementary colours is that their sum gives white light.
Answer:D. add-up to produce white light