【单选题】

Both plants and animals of many sorts show remarkable changes in form, structure, growth habits, and even mode of reproduction in becoming adapted to different climatic environment, types of food supply, or mode of living. This divergence in response to evolution is commonly expressed by altering the form and function of some part or parts of the organism, the original identity of which is clearly discernible. For example, the creeping foot of the snail is seen in related marine preemptors to be modified into a flapping organ useful for swimming, and is changed into prehensile arms that bear sartorial disks in the squids and other cephalopods. The limbs of various mammals are modified according to several different modes of life—for swift running (cursorial) as in the horse and antelope, for swinging to several different modes of life—for swinging in trees (arboreal) as in the monkey, for digging ( fossorial ) as in the moles and gophers, for flying (volant) as in the bats, for swimming (aquatic) as in the seals, whales and dolphins, and for other adaptations. The structures or organs that show main change in connection with this adaptive divergence are commonly identified readily as homologous, in spite of great alterations. Thus, the fingers and wrist bones of a bat and whale, for instance, have virtually nothing in common except that they are definitely equivalent elements of the mammalian limB、

The best title for this passage is ______.AdoptiveDivergence
B．Evolution
C．Unusual Structures
D．Changes in Organs