两栖动物在进化过程中占有重要的地位,这是因为两栖动物能证明动物进化的一个关键环节是[ ]
A.由低等到高等
B.由水生到陆生
C.由单细胞到多细胞
D.由简单到复杂
答案:B
On January 5, the U. S. Federal Reserve (the Fed) bought $10000000 of U. S. Treasury securities in the open market. At the time, the reserve requirement was 25 percent, and all banks had zero excess reserves. What is the potential impact of the Fed’ s purchase on the U. S. money supply()
A. $ 25000000 decrease.
B. $ 40000000 increase.
C. $ 10000000 increase.
引起院内感染最常见的病原体是()
A.真菌
B.螺旋体
C.病毒
D.立克次体
E.细菌