单选题乳腺小叶原位癌的特点是

单选题破裂性出血常见于

单选题下列符合变性的描述是

单选题脂褐素大量增加最常见于

单选题下列对于血管壁玻璃样变性，不恰当的描述是

单选题造血微环境是指

单选题安静时，正常机体能量代谢最为稳定的环境温度为

单选题 女阴结核感染途径中下列哪种最少见？（ ） A、输卵管播散 B、子宫内膜播散 C、受染月经血接种 D、血行播散 E、性接触

单选题哪种是恶性肿瘤

单选题纤维性修复过程最重要的细胞成分是（ ）

单选题干酪样坏死与普通凝固性坏死的主要不同点在于（ ）

单选题必要时，能转变为巨噬细胞的神经胶质细胞是

单选题细胞内外正常的Na + 和K + 浓度差的形成和维持是由于

单选题In the two decades between 1910 and 1930, over ten percent of the Black population of the United States left the South, where the majority of the Black population had been located, and migrated to northern states, with the largest number moving, it is claimed, between 1916 and 1918. It has been frequently assumed, but not proved, that most of the migrants in what has come to be called the Great Migration came from rural areas and were motivated by two concurrent factors: the collapse of cotton industry following boll weevil infestation, which began in 1898, and increased demand in the North for labor following the cessation of European immigration caused by the outbreak of the First World War in 1914. This assumption has led to the conclusion that the migrants' subsequent lack of economic mobility in the North is tied to rural background, a background that implies unfamiliarity with urban living and a lack of industrial skills. But the question of who actually left the South has never been investigated in detail. Although numerous investigations document a flight from rural southern areas to southern cities prior to the Great Migration, no one has considered whether the same migrants then moved on to northern cities. In 1910 over 600,000 Black workers, or ten percent of the Black work force reported themselves to be engaged in "manufacturing and mechanical pursuits", the federal census category roughly including the entire industrial sector. The Great Migration could easily have been made up entirely of this group and their families. It is perhaps surprising to argue that an employed population could be tempted to move, but an explanation lies in the labor conditions then prevalent in the South. About thirty-five percent of the urban Black population in the South was engaged in skilled trades. Some were from the old artisan class of slavery--blacksmiths, masons, carpenters--which had a monopoly of certain trades, but they were gradually being pushed out by competition, mechanization, and obsolescence. The remaining sixty-five percent, more recently urbanized, worked in newly developed industries--tobacco, lumber, coal and iron manufacture, and railroads. Wages in the South, however, were low, and Black workers were aware, through labor recruiters and the Black press, that they could earn more even as unskilled workers in the North than they could as artisans in the South. After the boll weevil infestation, urban Black workers faced competition from the continuing influx of both Black and White rural workers, who were driven to undercut the wages formerly paid for industrial jobs. Thus, a move north would be seen as advantageous to a group that was already urbanized and steadily employed, and the easy conclusion tying their subsequent economic problems in the North to their rural backgrounds comes into question.

单选题有关亚急性感染性心内膜炎的描述，哪项是错误的

单选题分泌突然增加而诱发排卵的激素是

单选题大肠杆菌DNA指导的RNA聚合酶由数个亚单位组成，其核心酶的组成是

单选题一般认为，外周血白细胞计数主要反映

单选题在测定基础代谢率的注意事项中，不正确的是

单选题甲状腺功能低下时大量透明质酸沉积于皮下，这种病变属于（ ）