Hemophilia results when a gene fails to produce the protein  needed for the blood to clot  ,or change from a liquid to a solid .The fault gene is passed from parents to children .People with hemophilia suffer uncontrolled bleeding .This can result in pain , tissue swelling  and permanent damage to joints and muscles.     One in every ten thousand males has the most common kind of hemophilia .It is extremely rare for females to have it. Patients can be treated with the missing clotting substance .They generally can lead normal lives.     Scientists say gene treatment may be a possible way to cure hemophilia in the future .Researchers consider hemophilia the best disease for gene treatment because it is caused by a single fault gene .Also ,only a small increase in the missing clotting substance could provide good results .They tested gene treatment in six patients with severe hemophilia.     First ,they removed skin cells from the patients' arms .The researchers grew the cells in the laboratory .They added copies of the needed gene taken from healthy people .Then they created hundreds of millions of genetically changed cells .They placed these cells into the patients' stomachs.After four months ,the amount of blood clotting substance in the blood increased in four of the six patients .Some of the patients reported a decrease in bleeding problems .However ,ten months later ,the clotting substance was no longer in the patients' blood .It is not clear if the implanted cells died or the added genes stopped working.     The researchers say the study showed that gene treatment is safe for people with the most common kind of hemophilia .But others expressed concern about the treatment because the effects were only temporary. People with hemophilia can live normally when  _  .
they are treated with the missing clotting substance they accept scientists' help good copies of gene are placed in their bodies They place some genetically changed cells into their stomachs
Question: Hemophilia results when a gene fails to produce the protein  needed for the blood to clot  ,or change from a liquid to a solid .The fault gene is passed from parents to children .People with hemophilia suffer uncontrolled bleeding .This can result in pain , tissue swelling  and permanent damage to joints and muscles.     One in every ten thousand males has the most common kind of hemophilia .It is extremely rare for females to have it. Patients can be treated with the missing clotting substance .They generally can lead normal lives.     Scientists say gene treatment may be a possible way to cure hemophilia in the future .Researchers consider hemophilia the best disease for gene treatment because it is caused by a single fault gene .Also ,only a small increase in the missing clotting substance could provide good results .They tested gene treatment in six patients with severe hemophilia.     First ,they removed skin cells from the patients' arms .The researchers grew the cells in the laboratory .They added copies of the needed gene taken from healthy people .Then they created hundreds of millions of genetically changed cells .They placed these cells into the patients' stomachs.After four months ,the amount of blood clotting substance in the blood increased in four of the six patients .Some of the patients reported a decrease in bleeding problems .However ,ten months later ,the clotting substance was no longer in the patients' blood .It is not clear if the implanted cells died or the added genes stopped working.     The researchers say the study showed that gene treatment is safe for people with the most common kind of hemophilia .But others expressed concern about the treatment because the effects were only temporary. People with hemophilia can live normally when  _  .
A. they are treated with the missing clotting substance
B. they accept scientists' help
C. good copies of gene are placed in their bodies
D. They place some genetically changed cells into their stomachs
Answer: