B
题意:
根据第4段,异种器官移植的主要问题是什么?
A.病人的想法。B.身体的排斥。C.价格高。D.器官的数量。
根据第四段Doctors have experimented(试验)with xenotransplantation since the early20th century. There are few success stories. Usually, patients' bodies reject(排斥) the animal organs. Bennett lived much longer than other xenotransplantation patients. That's because scientists removed(去掉) pig genes(基因) that would cause fast rejection. Then they added human genes to help the body accept the organ. 自20世纪初以来,医生们就开始试验异种器官移植。很少有成功的故事。通常,病人的身体会排斥动物器官。贝内特比其他异种移植患者活得更长。这是因为科学家们移除了会导致快速排异反应的猪基因。然后他们添加了人类基因来帮助身体接受器官。可知,异种器官移植的主要问题是身体的排斥,故选B。