However weak we are, we can still do something against the powerful nature as long as we are ______ prepared.

When the exam is over, you should hand in your exam papers, finished or _____. 

—Mom，dad is smoking again!—Well，let him cut it ________ gradually since old habits die hard.

To children, good habits do not come        , so parents and teachers need to be their role models.

The students are ___ young people between the age of sixteen and twenty.