（a） a regular class will be given.
（b） an optional review class will be given.
（c） an exam will be given.
（d） class will be canceled.
42.
（a） rock formations in the nevada desert.
（b） graduate studies in anthropology.
（c） excavation techniques used in archaeology.
（d） prehistoric desert people of nevada.
43.
（a） they planned their migrations.来源：考试大
（b） they didn't travel far from their base camps.
（c） they hid from their enemies in caves.
（d） they planted seeds near their camps.
44.
（a） they had trouble finding it.
（b） lack of light made it impossible.
（c） it was too small for a group to fit into.
（d） items stored by others took up most of the space.
45.
（a） prehistoric desert people.
（b） migratory animals.
（c） food supplies and tools.
（d） growing plants.
46.
（a） to illustrate the size of some objects.
（b） to introduce the next assignment.
（c） to show some artifacts on display at the campus museum.
（d） to demonstrate his photographic ability.
47.
（a） a comparison of fish to warm-blooded animals.
（b） the difference between saltwater and freshwater environments.
（c） the importance of fish to human beings.
（d） how water has affected the development of fish.
48.
（a） it can' t be compressed.
（b） it is often polluted.
（c） its temperature often fluctuates dramatically.
（d） it limits their size.
49.
（a） a whale.
（b） a human.
（c） a snake.
（d） a snail.
50.
（a） its skeleton.
（b） its shape.
（c） its senses.
（d） its body temperature.
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