It is well known to all that a machine needs fuel to run;    ,man needs food to live on.

He began to take political science ____ only when he leftschool.

 If a person has not had enough sleep, his actions will give him ___ during the day.

It isn’t so much whether he works hard; the question is whether he works _____.

A society cannot be successful if it throws tradition away, but it cannot be successful ____if we do something to stop progress.