题目内容：

    Gene therapy (基因治疗) is a revolutionary new technique for treating people with health problems. Up until very recently, the most commonly available methods for treating patients were either through drugs or operations. Gene therapy provides a third option for treatment by transforming or replacing cells with new genetic materials and instructions. Scientists can be very precise in the kinds of changes they make in patients.

Gene therapy works by using a delivery system, such as a virus, to enter a patient's body. Once inside the body, the virus combines with a host cell and delivers the new DNA. The proteins then begin to repair the affected cells. New techniques have focused on removing cells from the patients and transforming them outside the body before reintroducing them to the patients.

The two types of gene therapy are called somatic and germline. Somatic therapy refers to changing or replacing a body cell. In this case, the treatment is restricted to the patient only. This will not affect the patient's future children because the patient's germ (生殖) cells are unaffected. In germline therapy, the patient germ cells are treated, which may affect the patient's future generation.This is highly controversial (有争议的) because it is not clear exactly how this might affect them and further generations. For this reason, many countries have passed laws that prohibit this kind of treatment.

Despite the promise of gene therapy, there are still many barriers that need to be overcome before it comes into widespread use. One of the issues is that the use of viruses to deliver DNA may actually cause unexpected problems in patients if the virus grows and attacks the body. Another problem is the nature of many diseases is very complex and spread throughout multiple genes. The use of gene therapy to change a single gene in the body would probably not be sufficient as a cure. Finally, the costs of gene therapy are high. Some gene therapy procedures may cost over$1 million to undertake and require specialized doctors and equipment.

1.What does the underlined word ''them'' in paragraph 2 refer to?

A.Techniques. B.Cells. C.Patients. D.Proteins.

2.What can we learn about gene therapy?

A.Gene therapy has been put into practice widely.

B.The cells of patients are developed in healthy people.

C.Viruses entering the body can mix with host cells and form new DNA.

D.Both somatic and germline therapy have side effects on later generations.

3.What's the last paragraph mainly about?

A.The disadvantages of gene therapy.

B.The promising future of gene therapy.

C.The high costs of treatment procedures.

D.The issues related to viruses and complex genes.

4.What can be a suitable title for the text?

A.Why Gene Therapy Procedures Are Extremely Expensive

B.Gene Therapy: A Dangerous New After-operation Treatment

C.Gene Therapy: A Contemporary Progressive Treating Method

D.Scientists Are Accurate in Performing the Categories of Surgery