单选题
In the Arizona desert, tomatoes hang from ceilings, spinach grows without soil and shrimp lire in indoor pools. What's going on.'? Food research! People perform these experiments to learn how to produce more food. There will be over 6.5 bil- lion people on earth after two decades. We will have to produce four times as much food as we do now to feed all these people. But each year there is less fresh water, the soil loses nutrients and buildings take up more land. We must learn to use resources we have always thought unusable. So, the Environ- mental Research Laboratory in Arizona tries to grow food without soil, in the desert, and with salt water. So far the results have been excellent. The new methods yield twenty times more tomatoes and cu-cumbers than can be grown on a farm. About sixty times as many shrimp can be raised in indoors pools than ten boats can catch in the ocean in a year. Crops can grow in salty soil. Plus, as they grow, they take salt and minerals from desert soil, to create more useable land. The University of Arizona runs the research center in Arizona. But there are centers all over the world. Because of the promising results, big companies pay for some of the research. With interest and money backing them, researchers can go far. Their aim is to use wasted land and water to feed humanity. In the Arizona desert, they are off to a great start.