Which arrangement is correct for obtaining an objective result in an acrylic technique experiment?

Correct answer: Keep the surface and sample size constant while changing one variable at a time

The governing concept is controlled comparison. To identify whether a medium, dilution, brush, or layer causes a visual difference, the other conditions must remain constant. Changing one variable at a time and recording the samples makes the result traceable, so option A is correct. If everything changes, or no records are kept, the cause cannot be identified reliably.