If a dry tertiary-colour sample appears darker than the wet sample what should be the next step?

Correct answer: Make the next mixture slightly lighter

The governing concept is dry-colour adjustment: paint can appear different after water or binder evaporates. Since the dried sample is darker than intended, the next mixture should contain a little more lightening medium or a slightly smaller amount of strong pigment. Option A is correct because it compensates for the observed change. Adding black would darken it further, increasing an opposite colour may dull the hue, and repeating the same untested mixture ignores the evidence from the dry sample.