The work for which Thomas Malthus is still most widely known is his Essay on the Principle of Population, which first appeared in 1798. This book introduced Malthus’s __67__ that population inescapably outgrows subsistence (生活资料), and that this difference __68__ population size and the ability to adequately meet the __69__ subsistence needs of all the members of that population " naturally" produces a fundamental struggle for __70__ in which some flourish at the __71__ of others. Charles Darwin’s most important contribution __72__ the field of biology, described in his work. On the Origin of Species, was to __73__ Malthus’s observation that plants and animals multiply faster than nature can provide for them to his own __74__ of the process of "evolution" - the notion that different forms of life develop __75__ from a common ancestry (祖先). Combining these elements, Darwin __76__ that the factors of "the struggle for existence" and "the survival of the fittest" are the central mechanisms __77__ which evolution is based. In this sense, then. Darwin introduced the possibility __78__ conflict and struggle are biological phenomena, which are __79__ central to human social existence. A number of more contemporary social thinkers were __80__ by Darwin and continued this particular version of the conflict perspective, commonly referred to __81__ social Darwinism, into the twentieth century-Thus, for example, Herbert Spencer, a __82__ English social theorist, applied these ideas of the natural __83__ of conflict and survival of the fittest to his . notion of social evolution, __84__ William Graham Summer, an American sociologist, saw the __85__ for survival among individual actors as operating to bring about fundamental __86__ in the quality of human social life overall. 86（）

A. opportunities
B. advances
C. adventures
D. oppositions