单项选择题 The ideal gas goes through the cycle process as shown in the solid line in the figure. The two isochoric lines are respectively tangent to the cycle process curve at points a and c.The two isothermal lines are tangent to the cycle curve at points b and d. a, b, c and d divide the cycle into four stages: ab, bc, cd and da. Therefore, the exothermic stage in the four stages can be identified as ________ from the figure.

单项选择题 将一枚硬币重复掷n次，以X和Y分别表示正面向上和反面向上的次数，则X和Y的相关系数等于    (A) -1．    (B) 0．    (C) ．    (D) 1．

判断题 如果某锂离子电池的工作电压是从2.5V到4.2V,当电压小于2.5V时,电池也可以继续放电。() A、正确 B、错误