-I want to see Mr. White. We have an appointment.
-I'm sorry, but he is not ________ at the moment, for the meeting hasn't ended.
busy
active
concerned
available
The students listened carefully to the teacher with their eyes _____ on the blackboard.
With our knowledge practice , we can make contribution to our society.
The most popular food ______ on menus in western countries is hamburger.
There is no greater pleasure than running on the playground, ____ after a ball.
I tried all I could_____ the topic at the meeting, but he brought it up.