Answer is D. Mammals can produce milk for their offspring.
Mammals are the vertebrate which have some distinguishing features. Female mammals have mammary glands. Mammals got their name from this unique feature. Mammary glands are evolved from the modification of sweat glands. Mammary glands produce milk for their offspring. presence of hair on the body is also a defining feature of mammals. These defining features are not present in most of the vertebrates.