计算电缆敷设工作量时，其定额是按（）芯电缆设定的。
A、3
B、4
C、5
D、2
参考答案：A
质量为M、内壁间距为L的箱子静止于光滑的水平面上，箱子中间有一质量为m的小物块，小物块与箱子底板间的动摩擦因数为μ。初始时小物块停在箱子正中间，如图所示。现给小物块一水平向右的初速度v，小物块与箱壁碰撞N次后恰又回到箱子正中间，且与箱子保持相对静止。设碰撞都是弹性的，可用动量守恒mv=(m+M)V共求解共同速度，则整个过程中，以下说法正确的是
A．物块损失的动能为
B．系统损失的动能为
C．系统产生的内能为
D．系统产生的内能为
Complete the dialogue with proper words or sentences.
(Li Lei and Zhang Hai are talking on the phone.)
L-Li Lei.Z-Zhang Hai
L: Hello, Zhang Hai! I haven't heard from you for a long time. (1)______________?
Z: I'm preparing (准备) for the final exams.
L: Good luck to you!Summer holiday is coming. (2)______________?
Z: First, I'll have a good rest, and then I will go to Beijing to watch the Olympic Games.
L: (3)______________.
Z: Wonderful! Our plans are almost the same.
L: Are you going to visit some places of interest?
Z: (4)______________. I want to visit the Great Wall.
L: Let's meet in Beijing. We may do something useful to support the Olympics together.
Z: Sounds great.
L: See you then.
Z: (5)______________.
