储油期间定期检查油罐罐壁（）的是否完好，有无严重锈蚀、腐蚀等情况。
A.防腐层
B.防漏层
C.保温层
D.保护层
参考答案：A
一横截面为正方形的砖柱分为上下两段，如图所示。已知P=40kN，则荷载引起的最大工作应力为（）MPa。
A．0.69
B．0.96
C．0.78
D．0.88
A nursery sells trees of different types and heights. Suppose that 75 pine trees are sold for planting at City Hall. These 75 trees average 60 inches in height with a standard deviation of 16 inches. Using this information, construct a 95 percent confidence interval for the mean height of all trees in the nursery:（）
A. 60±1.96(16).
B. 0.8±1.96(16).
C. 60±1.96(1.85).
