垫片密封的主要结构不包括下列哪一项?()
A.螺母
B.螺栓
C.垫片
D.弹簧
参考答案:D
—________ shall we paint the walls?
— I prefer white. It makes us feel calm and peaceful.[ ]
A. How
B. How often
C. Why
D. What colour
既能升高血钙,又能降低血磷的物质是()。
A.维生素D
B.PTH
C.CT
D.ADH
E.甲状腺素