(1950-1980)

　　Year Population Housing Units

　　1950 500, 000 214, 000

　　1960 476, 000 218, 000

　　1970 453, 000 226, 000

　　1980 425, 000 237, 000

　　Which of the following, if true, most helps to reconcile the increase in housing units with the decline in population shown in the table above?

　　(A) The percentage of families that included adult children living at home increased during the 1970's.

　　(B) The number of people moving to Grand City from other cities gradually decreased during the three decades.

　　(C) The number of housing units that were vacant in Grand City fell steadily between 1950 and 1980.

　　(D) The number of adults who lived alone in Grand City housing units increased dramatically between 1950 and 1980.

　　(E) Many housing units that were occupied by only one family in 1950 were occupied by two or more families in 1980.

　　24. Fossils of the coral Acrocora palmata that date from the last period when glaciers grew and consequently spread from the polar regions are found at ocean depths far greater than those at which A. palmata can now survive. Therefore, although the fossilized A. palmata appears indistinguishable from A. palmata now living, it must have differed in important respects to have been able to live in deep water. The argument depends on the assumption that

　　(A) no fossils of the coral A. palmata have been found that date from periods when glaciers were not spreading from the polar regions

　　(B) geological disturbances since the last period during which glaciers spread have caused no major downward shift in the location of A. palmata fossils

　　(C) A. palmata now live in shallow waters in most of the same geographical regions as those in which deep-lying A. palmata fossils have been found

　　(D) A. palmata fossils have been found that date from each of the periods during which glaciers are known to have spread from the polar region

　　(E) A. palmata can live at greater depths where the ocean temperature is colder than they can where the ocean temperature is warmer

　　25.Conservationists have believed that by concentrating their preservation efforts on habitats rich in an easily surveyed group of species, such as birds, they would thereby be preserving areas rich in overall species diversity. This belief rests on a view that a geographical area rich in one group of species will also be rich in the other groups characteristic of the entire regional climate zone. Which of the following findings about widely scattered tracts

　　10 kilometers by 10 kilometers in a temperate climate zone would most seriously challenge the conservationists' assumptions?

　　(A) The tracts show little damage from human intrusion and from pollution by human activities.

　　(B) Where a certain group of species, such as birds, is abundant, there is also an abundance of the species, such as insects, on which that group of species feeds, or in the case of plants, of the land and water resources it requires.

　　(C) The area of one of the tracts is generally large enough to contain a representative sample of the organisms in the region.

　　(D) There is little overlap between the list of tracts that are rich in species of butterflies and the list of those that are rich in species of birds.

　　(E) The highest concentration of individuals of rare species is found where the general diversity of species is greatest.