In summer milk will quickly go bad _________ it is put into a fridge (冰箱).

You______ to the meeting this afternoon if you have something important to do.

Recently many people have no intention of buying a house— I think the reason may be ______ the house price is too high

cientist spent years alone in the forest, ______ by eating wild fruit and small animals.

As teenagers of the 21st century, we should be ready to _____ the challenge of society.