单选题 {{B}}Directions:{{/B}} There are 5 reading passages in this part. Each
passage is followed by some questions or unfinished statements. Fox' each of
them there are four choices marked A, B, C, and D. You should decide on the best
choice and mark your answer on the ANSWER SHEET by blackening the corresponding
letter in the brackets.
The opposite of adaptive divergence is
an interesting and fairly common expression of evolution. Whereas related groups
of organisms take on widely different characters in becoming adapted to unlike
environments in the case of adaptive divergence. We find that Unrelated groups
of organisms exhibit adaptive convergence when they spot similar modes of life
or become suited for special sorts of environments. For example,
invertebrate marine animals living firmly attached to the sea bottom or to some
foreign object tend to develop a sub- cylindrical or conical form. This is
illustrated by coral individuals, by many sponges, and even by the diminutive
tubes of bryozoans. Adaptive convergence in taking this coral-like form is shown
by some brachiopods and pelecypods that grew in fixed position. More readily
appreciated is the streamlined fitness of most fishes for moving swiftly through
water; they have no neck, the contour of the body is smoothly curved so as to
give minimum resistance, and the chief propelling organ is a powerful tail fin.
The fact that some fossil reptiles (ichthyosaurs) and modem mammals (whales,
dolphins) are wholly fishlike in form is an expression of adaptive convergence,
for these air-breathing reptiles and mammals, which are highly efficient
swimmers, are not closely related to fishes. Unrelated or distantly
related organisms that develop similarity of form are sometimes designated as
homeomorphs (having same form).
单选题
Organisms that could be classified as homeomorphs are ______.