What is the difference between adding black and adding blue-violet to yellow-orange?

Correct answer: Black darkens value while blue-violet reduces saturation

The governing concept separates a shade from a muted colour. Black lowers the value of yellow-orange and produces a darker shade. Blue-violet is near the complementary region of yellow-orange, so mixing a little of it tends to neutralise or reduce the colour’s saturation rather than simply darken it. Thus A correctly contrasts value change with intensity change; the other choices reverse or deny these colour relationships.