题目

 How will our continuously growing population affect our way of life, our environment, even our planet? No matter how you look at it, we will face 41_extremely serious problem. By the middle of the 21st century, we 42_(use) up all the oil that drives our cars if at the rate we’re going. Even if scientists develop some new 43_(way)of feeding the human race, the crowded conditions on the earth will make 44_necessary for us to look for open space somewhere else. But none of the planets in our solar system are able 45_(support) life at present. One possible solution 46_the problem, how计算：(结果用假分数表示） ．