In tuning system, the Federal Communications Commission had distributed parts of __ spectrum to 12 television channels which were broken into two groups to avoid interference with existing services at the beginning.

旅游散客()旅游投诉

______(不是在一段时间内只力图拯救一个物种), they are trying to save a complete natural environment.

Teamwork is essential on this course．

For Christians, Easter eggs symbolize______.

Leukemia

Leukemia is the most common type of 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 don't work the way they're supposed to. (47) The abnormal white blood cells multiply out of control, filling the 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 body's tissues) and platelets (that allow blood to clot)—are also crowded out by the white blood cells of leukemia. These cancer cells may also move to other parts of the body, including the bloodstream, where they continue to multiply and build up.

Although leukemia can make kids sick, most of the time it is treatable, and kids get better. Almost 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 to feel better.

Some children with leukemia will also have radiation therapy, too. (49)

If the cancer isn't getting better from usual amounts of chemotherapy and radiation, then a kid with leukemia Will probably need more treatment—with higher doses of chemotherapy and radiation to finally kill the cancer cells. But this heavy-duty treatment will also harm the normal cells in the kid's bone marrow too, and the bone marrow will no longer be able to produce normal blood ceils. So, doctors will then give a kid—or anyone else with bone marrow that is no longer working—normal bone 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 kid's 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 ceils are first made.

E. They don't protect the person from infections very well.

F. Radiation therapy uses invisible high-energy waves (similar to X-rays) to kill cancerous cells.

(46)