钠是一种（）性质的物品。
A、易燃固体
B、遇湿易燃物品
C、易燃液体
D、不燃气体
参考答案：B
He ________ his homework ________ the weekend. [ ]
A. don't do, at
B. doesn't do, at
C. isn't do, on
D. does, of
求测量值的算术平均值可以消除偶然误差。( )
