根据材料回答下列各题： Leukemia Leukemia is the most common type o{ cancer kids get, but it is still very rare. Leukemia involves the blood and blood-forming organs, such as the bone marrow. __________ (46) A kid with leukemia produces lots of abnormal white blood cells in the bone marrow. Usually, white blood cells fight infection, but the white blood cells in a person with leukemia dont work theway theyre supposed to. __________(47) The abnormal white blood cells multiply out of control, fillingthe bone marrow and making it hard for enough normal, infection-fighting white blood.cells to form.Other blood cells—such as red blood cells (that carry oxygen in the blood to the bodys tissues) andplatelets (that allow blood to clot)—are also crowded out by the white blood cells of leukemia. Thesecancer cells may also move to other parts of the body, including the bloodstream, where they continueto multiply and build up. Although leukemia can make kids sick, most of the time it is treatable, and kids get better. Al-most all leukemia patients are treated with chemotherapy, which means using anti-cancer drugs.__________ (48)Chemotherapy quickly goes to work, traveling through the blood to the bone marrow.There, the drugs can attack the cancer cells. After several weeks of chemotherapy, many kids begin tofeel better. Some children with leukemia will also have to have radiation therapy, too.__________(49) If the cancer isnt getting better from using the usual amounts of chemotherapy and radiation,then a kid with leukemia will probably need more treatment--with higher doses of chemotherapy andradiation finally kill the cancer cells. But this heavy-duty treatment will also har the normal cells inthe kids bone marrow too, and the bone marrow will no lohger be able to produce normal blood cells.So, doctors will then give a kid or anyone else with bone marrow that is no longer working normalbone marrow tissue from someone else who is healthy.__________(50) A. The chemotherapy drugs are given through a catheter, a narrow tube that is inserted into a blood vessel, sometimes in the kids upper chest. B. Early symptoms of leukemia are often overlooked, since they may resemble symptoms of the flu or other common diseases. C. This is a special procedure called a bone marrow transplant, and it helps the patient make new blood cells so they can recover from the leukemia. D. Bone marrow is the innermost part of some bones where blood cells are first made.E. They dont protect the person from infections very well. F. Radiation therapy uses invisible high-energy waves (similar to X-rays) to kill cancerous cells. __________