Five cloned pigs，whose organs are much less likely to be rejected(排斥) by a patient，have been born in the U．S. More than 62,000 people in the U．S. alone are waiting to ____ donated hearts，lungs and so on.The number of human donors falls far short of ____.Pig organs are of a(n) ____ size to human organs，and some scientists hope they might be used to help meet the ____.But previous attempts to transplant pig tissue into humans have ____. The five pigs ____ a gene that adds a sugar to the surface of pig cells.The sugar would ____ immune(免疫的) rejection of the tissue.“This advance provides a near­time ____ for overcoming the problem that there is not enough human organs for transplants，”says an expert.“This is the ____ gene for overcoming the ____ stage of rejection.” ____，scientists warn that much more work is necessary ____ organs from copies of the pigs could be transplanted into humans.Human genes will need to be added，to ____ rejection of the organ in the long term.There are also ____ that pig viruses could infect patients. Cloning techniques were ____ to the production of the pigs.Genes can only be knocked out(去除) in a single cell.Cloning of these single cells then allowed the ____ of a whole animal in which the gene was knocked out in every cell.But the PPL researchers have ____ in knocking out only one copy of the gene.The team will now attempt to knock out both copies of the gene. The team will also ____ tests to investigate whether a virus from the pigs could infect human cells.“Although a lot of the work is very ____，we’re still very far off being able to grow an organ，” says Julia，who is working on this project and quite ____ to creating similar knock­out pigs with researchers at the University of Missouri. 小题1: A．exchange B．check C．possess D．receive 小题2: A．discussion B．demand C．doubt D．distance 小题3: A．beneficial B．identical C．similar D．certain 小题4: A．shortage B．condition C．satisfaction D．argument 小题5: A．continued B．failed C．finished D．paused 小题6: A．lack B．include C．make D．change 小题7: A．leave B．cause C．block D．destroy 小题8: A．supply B．ambition C．contribution D．solution 小题9: A．only B．rare C．key D．safe 小题10: A．last B．whole C．next D．early 小题11: A．However B．Therefore C．Besides D．Finally 小题12: A．because B．before C．if D．after 小题13: A．prevent B．ignore C．judge D．weaken 小题14: A．regrets B．emotions C．concerns D．interests 小题15: A．simple B．vital C．unusual D．basic 小题16: A．collection B．application C．reception D．creation 小题17: A．delighted B．succeeded C．joined D．believed 小题18: A．conduct B．plan C．design D．study 小题19: A．perfect B．strange C．exciting D．disappointing 小题20: A．opposed B．used C．devoted D．suited