They .... playing basketball.
aren't
They ..... playing ping-pong.
aren't
Penguins are good at ....
swimming
What are they doing?
They're playing tennis.
Cheetahs are good at ....
running
What are they doing?
They're running.
They ..... swimming.
are
He is ..... gymnastic.
doing
He's .... a ball.
bouncing
He is ...... a ball.
catching
What are they doing?
They're playing volleyball.
Kangaroos are good at ....
jumping