students are required to take the boat race.

The prisoner of war wished to be _________. Ten years later, he ____ and went home.

Mary is always ready to do some __ work at the local geracomium（敬老院）in her spare time.

Do remember to be________. We must avoid any possible risks when doing this dangerous chemical experiment—burns, poisonous gases or cuts from broken tubes.

If the wild animals wander onto _____ land, the landowner may require the government to get them back．