2. 外语
  3. Two techniques have recently been developed to simplify research and reduce the number of nonhuman primates needed in studies of

Two techniques have recently been developed to simplify research and reduce the number of nonhuman primates needed in studies of

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问题     Two techniques have recently been developed to simplify research and reduce the number of nonhuman primates needed in studies of certain complex hormonal reactions. One technique involves the culturing of primate pituitary cells and the cells of certain human turnouts. In the other, animal oviduct tissue is transplanted under the skin of laboratory primates.  Both culturing techniques complement existing methods of studying intact animals.
    With an in vitro culturing technique, researchers are deciphering how biochemical agents regulate the secretion of prolactin, the pituitary hormone that promotes milk production. The cultured cells survive for as long as a month, and they do not require serum, a commonly used culture ingredient that can influence cellular function and confound study results. One primate pituitary gland may yield enough cells for as many as 72 culture dishes, which otherwise would require as many animals.
    The other technique allows scientists to monitor cellular differentiation in the reproductive tracts of female monkeys. While falling short of the long-sought goal of developing an in vitro model of the female reproductive system, the next-best alternative was achieved. The method involves transplanting oviduct tissue to an easily accessible site under the skin, where the grafted cells behave exactly as if they were in their normal environment. In about 80 percent of the grafts, blood vessels in surrounding abdominal skin grow into and begin nourishing the oviduct tissue. Otherwise, the tissue is largely isolated, walled off by the surrounding skin. A cyst forms that shrinks and swells in tandem with stages of the menstrual cycle. With about 80 percent of the grafts re-establishing themselves in the new site, a single monkey may bear as many as 20 miniature oviducts that are easily accessible for study.  Because samples are removed with a simple procedure requiring only local anaesthesia, scientists can track changes in oviduct cells over short intervals. In contrast, repeated analysis of cellular changes within the oviduct itself would require abdominal surgery every time a sample was taken--a procedure that the animals could not tolerate.
    Scientists are using the grafting technique to study chlamydia infections, a leading cause of infertility among women. By infecting oviduct tissues transplanted into the abdominal skin of rhesus monkeys, researchers hope to determine how the bacteria cause pelvic inflammatory disease and lesions that obstruct the oviduct.  Such research could eventually lead to the development of antibodies to the infectious agent and a strategy for producing a chlamydia vaccine.  
It can be inferred from the passage that an in vitro model of the female reproductive system is ______.
选项 A、currently available but prohibitively expensive
B、currently available and widely used
C、theoretically possible but of no real scientific value
D、theoretically possible but as yet technically impossible
答案D
解析 根据短文可以推断，从理论上讲，雌性生殖系统的体外模型是可能存在的；但是，到目前为止，从技术的角度看，它是难以实现的。根据第三段第二句，嫁接技术不符合人们长期以来追求的、研制出体外模型的目标。根据这句话，我们首先可以推断，体外模型尚不存在。因此，可以排除A和B。其二，我们可以根据long-sought(长期寻求的)这个词进行推断。从科学的角度看，这样一个模型有可能存在，而且有实用价值。在此基础上，我们可以排除C。所以正确D。
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