阅读理解(阅读以下材料 回答第41——45题)Bone Marrow Transplantatio

阅读理解(阅读以下材料，回答第41——45题)

Bone Marrow Transplantation

Bone marrow is the spongy tissue inside some of your bones,such as your hip and thigh bones. It contains immature cells,called stem cells.The stem cells can develop into the red blood cells that carry oxygen through your body,the white blood cells that fight infections,and the platelets that help with blood clotting.

If there is a problem with your bone marrow,a transplant can give you healthy new marrow. You could need a transplant because of a disease,such as bone marrow diseases or cancers like leukemia kemia or lymphoma.Or you might need one if a strong cancer treatment kills your healthy blood cells.

People with cancer sometimes donate bone marrow before treatment to be transplanted later. But often the new marrow comes from a donor,either a close family member or someone unrelated.

The healthy cells for a transplant can come from three sources:bone marrow;peripheral (circulating) blood that has an increased number of healthy blood-forming cells(also called peripheral blood stem cells or PBSC);umbilical cord blood that is collected after a baby is born.

If you need an allogeneic transplant,your doctor will look for a marrow donor or cord blood unit that matches your HLA tissue type.HLA stands for human leukocyte antigen,a markei your immune system uses to recognize which cells belong in your body and which do not.

Before your body can receive the healthy cells,the diseased cells must be destroyed.This is done using chemotherapy and sometimes radiation. The destruction of diseased cells is called a preparative regimen or a conditioning regimen.

On the day of transplant,the cells from the marrow donor or cord blood unit are infused intravenously(go into your body through a large vein).These healthy cells move into the spaces inside your bones where they create new marrow. They grow and make healthy new red blood cells,white blood cells,and platelets.

The new marrow usually comes from__________.

A.people with cancer

B.a family member

C.an organ donor

D.a relative or a stranger