The correct answer is D. salivary glands of vertebrates.
Poison glands of snakes are homologous to salivary glands of vertebrates. This means that they share a common evolutionary origin, even though they have different functions in the two groups of animals.
Electric organs of fishes are not homologous to poison glands of snakes. Electric organs are used to stun or kill prey, while poison glands are used to defend against predators.
Stings of rays are not homologous to poison glands of snakes. Stings are used to inject venom into prey, while poison glands are used to secrete venom.
Sebaceous glands of mammals are not homologous to poison glands of snakes. Sebaceous glands produce sebum, an oily substance that helps to keep the skin and hair healthy. Poison glands produce venom, a toxic substance that can be used to defend against predators or kill prey.
In conclusion, the correct answer is D. salivary glands of vertebrates.