从19世纪30年代起，美国政府在几十年内建成了横贯大陆的（）条铁路干线。
A.3
B.4
C.5
D.6
参考答案：C
A client with myocardial infarction and cardiogenic shock is placed in an intra-aortic balloon pump (IABP). If the device is functioning properly, the balloon inflates when the（）
A. triseupid valve is closed.
B. pulmonic valve is open.
C. aortic valve is closed.
D. mitral valve is closed.
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