Ans.
Vestigial organs or structures are those structures that are no longer functional in current organisms, but were functional in their ancestral organisms. Examples of vestigial organs include appendix, hairs, and tailbone in humans.
-Tailbone in humans is a vestigial structure as humans do not have tails. Tailbones are functional in monkeys as they have long tails, which they used for balancing. Hence, 'tailbone in humans' correctly matches with 'balancing in monkeys.'
-Eyeballs in cavefish are vestigial organs as eyeballs are non-functional in cavefish. Cavefishes cannot see as they lost their sights during evolution as it is not necessary since they live in dark caves. Eyeballs are functional in whales as they provide eyesight to them. Hence, 'eyeballs in cavefish' correctly matches with 'sight in whales.'
-Pelvis bones in whales are vestigial structures as there is no role of these bones in whales. Pelvic bones are functional in frogs, as their limbs are attached to the body with the help of pelvic bones. Hence, 'pelvic bones in whales' correctly matches with 'attachment point for limbs in frogs.'