男性，32岁。发热、咽痛伴齿龈出血及乏力半个月。查体发现浅表淋巴结和脾脏轻度肿大。外周血象检查结果显示：Hb60g/L，WBC2．5×109/L，N0．52，PLT42×109／L，血涂片红细胞形态正常。骨髓有核细胞增生明显活跃，原始细胞0．46
如何解释该患者外周血白细胞数不增高，血片也未见幼稚细胞，可能的原因是（）
A.骨髓原始细胞数少，不能进入血循环
B.白血病合并粒细胞缺乏症
C.急性增生性白血病
D.急性低增生性白血病
E.白血病细胞分化成熟未受阻
参考答案：D
Choose the words or expressions to complete the passage(选择最恰当的单词或词语，完成短文) For many years the United States and the other countries used gold and silver as money. Paper money was used to stand for the holdings(储备)of both gold and silver. The value of silver was limited to that of gold. Fifteen ounces(盎司) of silver had the same value of one ounce of gold. These values did not change until after 1860 when mines(银矿)in the west of the United States began to 1 large amounts of silver. This extra amount of silver caused the price of silver to 2 . Then fifteen ounces of silver would no longer buy one ounce of gold. In 1871 Germany declared(宣布)that it would not support its paper money with silver any more. Instead, it would use only gold. Other countries of Europe quickly 3 the same. The United States passed a law in 1973 that prevented the government from using silver as money. Western silver producers protested(抗议)loudly and put much pressure on the 4 makers. Five years later a new law was 5 . It said that the government must buy four and half million ounces of silver each month. The new law increased the amount of silver money. The country had two kinds of quite different views on the issue(发行)silver money. Businessmen, bankers and other rich men wanted to 6 the use of silver money because it made the dollar less valuable. But farmers, laborers and the others who owned the money not only wanted silver money but also wanted an unlimited supply of it.  
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