第4部分：阅读理解（第31～45题，每题3分，共45分）
下面有3篇短文，每篇幅短文后有5道题，每题材后面有4个选项。请仔细阅读短文并根据短文回答其后面的问题，从4个选项中选择一个最佳答案涂在答题卡相应的位置上。
Ulcers
Even though ulcers appear to run in families, lifestyle plays more of role than genetic（基因的） factors in causing the illness, according to a report in the April 13th Journal of Internal Medicine. In particular, smoking and stress in men and the regular use of pain releasing medicines in women were linked with an increased risk of developing an ulcer（溃疡）.
Overall, 61% of ulcer risk appears to be due to environmental factors, such as smoking, and the remaining 39% is due to genes according to Dr. Ismo Raiha of the University of Turkey and colleagues at the University of Helsinki, Finland. Some researchers had suggested that families may spread Helicobacteria pylori（幽门螺旋菌）, the bacteria（细菌） that can cause ulcers. However, the new study suggests this is unlikely, according to the report.
Raiha and colleagues studied data from more than 13,000 pairs of twins "to examine the roles of genetic and environmental factors in the origin of peptic ulcer disease," they explain. Both twins were more likely to develop an ulcer if the pair were genetically the same as compared with a pair of fraternal（由两受精卵发育而成的） twins, suggesting that there must be some genetic susceptibility（敏感性） to ulcer development.
However, the risk was no greater in twins living together compared with twins living apart, suggesting that shared exposure to H. pylori was not to blame. "Environmental effects were not due to factors shared by family members, and they were related to smoking and stress in men and the use of analgesics in women," the authors wrote. "The minor effects of shared environment to disease liability do not support the concept that the grouping of risk factors, such as H. pylori infection, would explain the genetic factor of peptic ulcer disease," they concluded.
