because they do not want eat too much or another reasons.but i think we should not waste anthing for ang reason.wasting is a bad habit for us.we must move now.let us change now.we can do something to conserve.just like cleaning our paints and chosing exactly size food .eating all of them is a good idea.just some good ideas can make our life health.that's all.thanks for your listening.临时写的差不多了吧