硝酸镁蒸发器的加热蒸汽是（）。
A.高压蒸汽
B.中压蒸汽
C.低压蒸汽
D.超高压蒸汽
参考答案：B
（11分）一质量为2千克的铅球从离地面２米高处自由下落，陷入沙坑２厘米深处，求沙子对铅球的平均作用力（取g=10m/s2）
You were stupid to try climbing up there. You ______ yourself.
A．can kill
B．might have killed
C．might kill
D．must have killed
