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  3. The opposite of adaptive divergence is an interesting and fairly common expression of evolution. Whereas related groups of organ

The opposite of adaptive divergence is an interesting and fairly common expression of evolution. Whereas related groups of organ

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问题     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).  
Ichthyosaurs are ______.
选项 A、mammals that live in the sea
B、closely related to fishes
C、fossil reptiles
D、air-breathing animals
答案C
解析 鱼龙是化石爬行动物。文章的倒数第二句中提到了fossil reptile(化石爬行动物)，然后用括号将术语ichthyosaur(鱼龙)附在后面，这说明它们代表相同的动物。
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