d.) COLORFUL FLOWERS is the structural adaptation that some plants have to attract pollinators.
The more colorful the flowers are, the more insects are attracted to the flowers. Insects would then land on the flowers wherein the pollen in the flower will stick to the body of the insect. Insects are called pollinators. They help in the pollination of the flowers.
Pollination is the transfer of pollen from the flower's anthers to its stigma or another flower's stigma which will start up its fertilization.