Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.

It is a common saying that we do not fully value a thing until we lose it. We often value the love and worth of a friend when he has been taken from US by death more than when he was with US in the flesh; it is only when we have left school or college that we understand the greatness of our opportunity of education, which has gone forever; and it is the sick and the ailing who realize the value of good health, when we are young and strong, we cannot imagine what it is to be weak and ailing. We are so used to vigorous health that we take it for granted. The organs of our body work so smoothly that we scarcely know we have lungs and liver, heart and stomach. But when any of these gets upset and gives US pain and sickness, we learn by bitter experience what an unspeakable blessing it is to be well.

          Loss of health makes US miserable, and a burden to ourselves and our friends. It cripples our efforts so that we cannot accomplish many of the good and great things we might have done. It spoils our life. What must we do to keep our health?

          We must be moderate in eating and drinking and wise in the choice of plain, wholesome simple food. Gluttony has killed thousands, and strong drink tens of thousands. We must, when young, get plenty of sleep, which is "nature's sweet restorer", and not try to burn the candle at both ends. We must live as much as possible in the open air and keep our rooms well ventilated. We must get sufficient and regular physical exercise, and keep our bodies clean. And we must avoid bad habits and secret sins as we avoid the devil, and keep our thoughts clean and our bodies pure. Our ideal must be the sound mind in the sound body.

Accordingtothe passage, we often appreciate our friends________________.