8名同学排队检查视力情况，平均每人用2分钟，到最后一名同学检查完视力，他一共等了____分钟。

如图所示，平行板电容器的A板带正电，与静电计上的金属球相连；平行板电容器的B板和静电计的外壳均接地．此时静电计指针张开某一角度，则以下说法中正确的是（   ）

读“经纬网图”，完成下列问题．

随着中国经济的快速发展以及科技水平的飞速提高，中国高铁正迅速崛起．高铁大大缩短了时空距离，改变了人们的出行方式．如图，A，B两地被大山阻隔，由A地到B地需要绕行C地，若打通穿山隧道，建成A，B两地的直达高铁可以缩短从A地到B地的路程．已知：∠CAB=30°，∠CBA=45°，AC=640公里，求隧道打通后与打通前相比，从A地到B地的路程将约缩短多少公里？（参考数据： $\sqrt{3}$ ≈1.7， $\sqrt{2}$ ≈1.4）

从方框中选择最佳选项完成对话, 有两项多余。

A. Don't worry. B. Let's look for it together. C. What's the matter? D. Whose backpack is this? E. It can't be mine. F. You are welcome. G. I think I might leave it in the reading room.

A: Anna, you look worried. ____ 

B: I can't find my backpack anywhere. Where can it be?

A: ____ Let's see where it might be.

B: ____But it isn't there.

A: What color is your backpack? ____ 

B: It's black and white.

A: Oh, look! Is this one yours?

B: No. ____ Mine is newer than this one.