牵引术助产，胎儿通过骨盆腔时，牵引的方向应为（）
A.向上向后
B.水平向后拉
C.略向下拉
D.向后向下
E.向前向上
参考答案：B
Which of the following best explains the slope of the yield curve（）
A. The term spread between the yields of two maturities.
B. The credit spread between two securities with different maturities.
C. The nominal spread between two securities with different maturities.
对一般建筑负荷如空调、照明等进行市电供电的分配、通断控制、监测和保护的动力柜是（）
A.高压开关柜
B.市电油机转换屏
C.低压配电柜
D.ATS柜
