Tom and Mike are good friends. They are good with children. They want to find jobs in summer vacation. This Friday Tom tells Mike that Sunson School Trip needs teachers to help with sports, music and computer. Mike is glad to know that.
    Tom can play basketball, volleyball, and he can swim. Mike can play the violin, the trumpet, the drums and the guitar, and he can swim,too. Tom and Mike like computers very much. Can they join Sunson School Trip?

It's fantastic to work as           volunteer for the Special Olympics World Games.

下列生活情景中，通过做功来改变物体内能的是（　　）

设直线$l:x-2y+2=0$关于原点对称的直线为$l^{\text{'}}$，若$l^{\text{'}}$与椭圆$x^2+4y^2=4$的交点为P、Q, 点M为椭圆上的动点，则使△MPQ的面积为$\frac{1}{2}$的点M的个数为（）

B