—Don't forget _______ the lights. We should help save electricity.
A：turning off
B：to turn off
C：not to turn off
D：not turning off
若|a+2|=a+2，则a的取值范围是（ ）
---- _________ do you like ping-pong ?
---- Because it is relaxing.
用一个平面去截一个几何体，截面不可能是圆的几何体是（ ）
