A、It will grow 70%. B、It tends to be relatively stable. C、It is expected to decline. D、It could double. A文中说：联合国预测，本世纪中叶世界对粮食的需求

Organic farming avoids the use of chemical pesticides and man-made fertilizers. Supporters say organic farming is better for the environment than conventional methods. But studies have shown that organic farming generally produces less food per hectare.
    That lower yield means feeding the world organically would require more land. But good farmland is limited. And scientists say deforestation from the clearing of land for agriculture is already a problem for climate change.
    A new study shows organic crops typically yield less than those raised with artificial fertilizers and pesticides. In a new study, researchers wanted to measure the difference between conventional and organic yields. So they combined the results of sixty-six earlier studies. They found that some organic farms can yield almost as much as conventional farms. But most cannot.
    On average, organic farms produced twenty-five percent less compared to conventional farms. But yields of organic fruits and other perennial crops nearly equaled the yields from conventional ones. So did the yields of soybeans. The soil on organic farms holds water better, and that can reduce the yield difference. Also, organic farmers can improve their yields by making sure their crops get enough fertilizer.
    The United Nations predicts that world demand for food will grow seventy percent by the middle of the century. John Reganold, a soil scientist at Washington State University says no one should dismiss organic agriculture as part of the solution. Organic farming can’t feed the world. Conventional farming cannot sustainably feed the world. Farming is increasingly a combination of organic and conventional methods.
Q13: What is the disadvantage of organic farming?
Q14: What is the UN prediction of global demand for food by the middle of the century?
Q15: What might be the future trend of farming according to the soil scientist?