A study shows the students who are engaged in after-school activities are happier than _________who are not.
ones
those
these
them
Having taken our seats, _______.
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.