造成蒸发器安全阀起跳的原因，下列说法正确的是（）。
A、塔液位波动大
B、蒸汽加入量过多
C、蒸汽加入量过少
D、乙二醇浓度低
参考答案：B
车削工件材料为中碳钢的普通内螺纹，计算孔径尺寸的近似公式为______。
A．D孔=d-P
B．D孔=d-1.05P
C．D孔=d-1.0825P
The mother of a 9-month-old asks about adding new foods to his diet. The child is being breast-fed and takes formula and cereal when at the sitter's. Which of the following would the nurse instruct the mother to do
A．Mix new foods with formula or breast milk.
B．Mix new foods with more familiar foods.
C．Offer new foods one at a time.
D．Offer new foods after giving formula or breast milk.
