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請依下文回答第 46 題至第 50 題Umbilical cord blood was once discarded as waste material but is now known to be a useful source of blood stemcells. After a baby is born, cord blood is left in the umbilical cord and placenta. It is easy to collect, with no risk to themother or baby. It contains haematopoietic (blood) stem cells: rare cells normally found in the bone marrow.Haematopoietic stem cells (HSCs) can make every type of cell in the blood – red cells, white cells and platelets. Theyhave been used for many years in bone marrow transplants to treat blood diseases.Cord blood is used to treat children with cancerous blood disorders such as leukemia, or genetic blood diseaseslike Fanconi anemia. The cord blood is transplanted into the patient, where the HSCs can make new, healthy bloodcells to replace those damaged by the patient’s disease or by a medical treatment such as chemotherapy for cancer. Inthis way, cord blood offers a useful alternative to bone marrow transplants for some patients. It also seems to be lesslikely than bone marrow to cause immune rejection or complications such as Graft versus Host Disease.However, cord blood transplants also have limitations. Treatment of adults with cord blood has so far proved tobe very challenging, despite some successes. Cord blood can also only be used to treat blood diseases. No therapies fornon-blood-related diseases have yet been developed using HSCs from either cord blood or adult bone marrow. A majorlimitation of cord blood transplantation is that the blood obtained from a single umbilical cord does not contain asmany haematopoeitic stem cells as a bone marrow donation. A transplant containing too few HSCs may fail or couldlead to slow formation of new blood in the body in the early days after transplantation. This has been partiallyovercome by transplanting blood from two umbilical cords into larger children and adults. Some researchers have alsotried to increase the total number of HSCs obtained from each umbilical cord by collecting additional blood from theplacenta. Much research is focused on trying to increase the number of HSCs that can be obtained from one cord bloodsample by growing and multiplying the cells in the laboratory. This is known as “ex vivo expansion”. Severalpreliminary clinical trials using this technique are underway. The results so far are mixed: some results suggest that exvivo expansion reduces the time taken for new blood cells to appear in the body after transplantation; however, adultpatients still appear to need blood from two umbilical cords. Neither solution is entirely satisfactory.
46 What is the main idea of this passage?
(A)Cord blood is a panacea that can cure all diseases.
(B)Cord blood has a good application but it also has limitations.
(C)Cord blood treatment is only applicable to children.
(D)Cord blood is much easier and safer to collect than bone marrow.

參考答案

答案：B
難度：適中0.6
統計：A(3),B(12),C(3),D(2),E(0)

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