下列物质中，属于纯净物的是
A．茶饮料
B．蒸馏水
C．苹果醋
D．纯牛奶
答案：B
抛石防护具有柔韧性和整体性，在沉陷时能自由变形，一般用于（）工程。
A 16-year-old girl comes to the school nurse complaining of cramps, backache, and nausea with her periods. The nurse most likely would interpret these symptoms as which of the following（）
A. Pathologic.
B. Physiologic.
C. Psychogenic.
D. Psychosomatic.
