The deposits at Holzmaden， Germany， present an interesting case for analysis. The ichthyosaur remains are found in black， bituminous marine shales deposited about 190 million years ago. Over the years， thousands of specimens of marine reptiles， fish， and invertebrates have been recovered from these rocks. The quality of preservation is outstanding， but what is even more impressive is the number of ichthyosaur fossils containing preserved embryos. Ichthyosaurs with embryos have been reported from 6 different levels of the shale in a small area around Holzmaden， suggesting that a specific site was used by large numbers of ichthyosaurs repeatedly over time. The embryos are quite advanced in their physical develop- ment； their paddles， for example， are already well formed. One specimen is even preserved in the birth canal. In addition，the shale contains the remains of many newborns that are between 20 and 30 inches long.

　　Why are there so many pregnant females and young at Holzmaden when they are so rare elsewhere？ The quality of preservation is almost unmatched， and quarry operations have been carried out carefully with an awareness of the value of the fossils. But these factors do not account for the interesting question of how there came to be such a concentration of pregnant ichthyosaurs in a particular place very close to their time of giving birth.

　　23. The passage supports which of the following conclusions？

　　（A） Some species of ichthyosaurs decayed more rapidly than other species.

　　（B） Ichthyosaur newborns are smaller than other newborn marine reptiles.

　　（C） Ichthyosaurs were more advanced than terrestrial creatures.

　　（D） Ichthyosaurs may have gathered at Holzmaden to give birth.

　　24. The word "they" in line 4 refers to

　　（A） skeletons

　　（B） scavengers

　　（C） creatures

　　（D） environments

　　25. All of the following are mentioned as factors that encourage fossilization EXCEPT the

　　（A） speed of burial

　　（B） conditions of the water

　　（C） rate at which soft tissues decay

　　（D） cause of death of the animal.

　　26. Which of the following is true of the fossil deposits discussed in the passage？

　　（A） They include examples of newly discovered species.

　　（B） They contain large numbers of well-preserved specimens

　　（C） They are older than fossils found in other places

　　（D） They have been analyzed more carefully than other fossils.

　　27. The word "outstanding" in line 18 is closest in meaning to

　　（A） extensive

　　（B） surprising

　　（C） vertical

　　（D） excellent

　　28. The word "site" in line 22 is closest in meaning to

　　（A） example

　　（B） location

　　（C） development

　　（D） characteristic

　　29. Why does the author mention the specimen preserved in the birth canal （line 26）？

　　（A） To illustrate that the embryo fossils are quite advanced in their development

　　（B） To explain why the fossils are well preserved

　　（C） To indicate how the ichthyosaurs died

　　（D） To prove that ichthyosaurs are marine animals.