What is good to do before applying a mixed colour to the main artwork?

Correct answer: Test a sample on separate paper

The governing concept is testing and controlling a colour mixture before applying it to the final artwork. A small sample on separate paper reveals the mixture’s shade, thickness, coverage, and any noticeable change after drying. Therefore, option B is correct. Applying it directly could spoil a large area if the colour is too dark, pale, thick, or watery; the other choices do not provide a useful check.