What should be done to obtain a yellowish green?

Correct answer: Increase the amount of yellow

Green is formed by mixing blue and yellow pigments. To shift green toward yellow and obtain yellowish green, the proportion of yellow must be increased; therefore, option A is correct. Increasing blue would create bluish green. Adding red introduces another colour component and may dull the mixture, while black changes its value by darkening it rather than creating the desired yellow bias. The answer follows the dominance principle in colour mixing.