根据材料回答下列各题： 第一篇 Genetic Engineering Genetic ehgineering began when the DNA molecule(分子)，the most basic unit of life，was first described in l953 by James Watson and Francis Crick．An understanding of DNA led to the altering of normal cell reproduction．Experiments with altering human cells began in l970．In one of the first experiments，patients were injected with a virus that would produce a life—saving enzyme，but their bodies would not accept it．In l980 patients with a rare but fatal blood disease were injected with a purifled gene that was cloned through DNA technology．Another failure． Genetic engineering got a legal boost(激励)in l980．The U．S．Supreme Court said that a patent could be granted on a genetically engineered“oil—eating”bacterium(细菌)．This bacterium would help clean up oil spills．The ruling encouraged companies to invent new life forms，and three important medical products were quickly developed． Human interferon(干扰素)一a possible solution to some cancers and viral disease．A newly engineered bacterium produced human interferon as a by—product．This new product reduced the cost of interferon． Human growth hormone—for children whose bodies do not grow to normal height．An expensive growth hormone(荷尔蒙)was previously produced from human cadavers，but by changing the genetic make—up of the single—cell bacterium E．coli，and affordable growth hormone could be produced． Human insulin(胰岛素)一for the treatment of diabetes．People with diabetes used to rely on a beef-or pork—based product until l982．Now insulin can be manufactured by genetically altered bacteria． Advances in genetic engineering have continued，though they constantly must be weighted against the safety of procedures．There is clearly much more to discover． This passage is mainly about________．