Why can cyan be more useful than a traditional blue for producing a very clean green?

Correct answer: Cyan has less red bias

The governing concept is pigment colour bias in subtractive mixing. A traditional blue pigment may contain a slight red or violet bias; when mixed with yellow, that unwanted red component can muddy the green. Cyan is closer to a blue-green primary and has less red bias, so cyan plus yellow can reflect a cleaner green. It is not necessarily darker, pre-mixed with white, or always transparent; therefore option A is correct.