Lavender absorbs violet light.

A, purple lavender reflects purple light and absorbs other colors, so A is wrong;

B, reflection, which belongs to plane mirror imaging, is the reflection principle of light, so B is correct;

C, the shadow is formed because the light travels in a straight line and the body blocks the light. Therefore, C is correct;

D the rainbow is formed by the dispersion of light, so d is correct.

So choose a.