从方框中选择合适的选项补全对话。

A: Where have you been, Li Hai? I called you, but you weren't in.

B: ____

A: ____

B: I found that the factory was pouring waste water into the river near it. Lots of fish have died.

A: ____

B: Do you think “Greener China” can do something?

A: ____ if they know about this thing, they will prevent it. Let's write to them at once.

B: ____ I think everything will become better.

质量为m的小球由轻绳a和b分别系于一轻质细杆的A点和B点，如图，绳a与水平方向成θ角，绳b在水平方向且长为l，当轻杆绕轴AB以角速度ω匀速转动时，小球在水平面内做匀速圆周运动，则下列说法正确的是（   ）

如图所示几何体的俯视图是（　　）

口技演员能够模仿许多乐器和动物的声音，它主要是要模仿动物和乐器发出声音的（  ）