离心式压缩机常用的（）原动机，它具有结构简单、维修工作量小以及操作方便等优点。
A.汽轮机
B.燃汽轮机
C.电动机
D.发电机
参考答案：C
The evidence suggests that the correlation of returns between U.S. government bonds and an index of international government bonds is:（）
A. between 0.0 and -0.5, and that between indices of U. S. investment grade bonds is between 0.0 and 0.5.
B. between 0.0 and 0.5, and that between indices of U. S. investment grade bonds is close to 1.0.
C. between 0.0 and 0.5, and that between indices of U. S. investment grade bonds is between 0.25 and 0.75.
产后、手术后生殖器炎症及伤口感染常见的病原体为（）.
A.链球菌
B.葡萄球菌
C.大肠埃希菌
D.厌氧菌
E.衣原体
