四、閱讀測驗【請在下列各題中選出最適當的答案】第一篇：A new study provides scientific evidence to support the idea that stress can cause a person’s hair to turn gray. Ateam from America’s Harvard University said the new study is the first to show a clear link between stress and grayinghair. The findings were recently published in the journal Nature. Researchers say they discovered a chemical processthat can change hair color during times of stress. The process is linked to the body’s “fight-or-flight” reaction that canhappen during dangerous situations.Ya-Chieh Hsu is a professor of Stem Cell and Regenerative Biology at Harvard. She said in a statement that theresearch team was in search of the first scientific confirmation of the commonly held belief that stress can cause grayhair. “Everyone has an anecdote to share about how stress affects their body, particularly in their skin and hair - theonly tissues we can see from the outside,” Hsu said.The team used experiments with mice to look at how stress affects stem cells in hair follicles. Most people haveabout 100,000 hair follicles on their head. The follicles are responsible for making melanocytes, the cells that give hairits color. As people age, melanocyte production is reduced. This causes a person’s hair to begin turning gray naturally.At first, the researchers suspected that an immune attack caused by a stressful event might be targeting the melanocytestem cells. That theory, however, turned out to be false. The mice lacking immune cells still showed signs of grayinghair. The team also thought the hormone cortisol, which always increases in the body during times of stress, might be alikely cause. However, when researchers removed the gland that produces the cortisol hormones, the hair of mice stillturned gray.The scientists then centered their experiments on the body’s sympathetic nervous system. This is the body systemthat controls “fight-or-flight” reactions in dangerous situations. The sympathetic nervous system is made up of acollection of nerves that extend through the body, including the skin. When the mice were subjected to short-term painor placed in stressful laboratory conditions, these nerves released a chemical called norepinephrine. The chemical thenflowed through the stem cells up into the hair follicles -- where melanocytes are kept. The researchers found that whenthe norepinephrine was released, all the melanocyte stem cells were highly activated and changed intopigment-producing cells. This overproduction process resulted in the early loss of color-producing cells.Ya-Chieh Hsu said the experiments confirmed the team’s belief that stress is bad for the body. She added that theresults demonstrated the harmful effects are more major than what the researchers had imagined. “After just a few days,all of the pigment-regenerating stem cells were lost. Once they’re gone, you can’t regenerate pigments anymore. Thedamage is permanent,” Hsu said.The scientists said their research could lead to new treatments for stress-related graying in the future. Graying hairis just one example of how stress affects the body. New experiments could also be carried out in other areas as well, theteam said. These could include studies to see whether stress can also cause changes in body tissues. Hsu said she wouldalso like to study whether stress has a large effect on the overall aging process. “We don’t know if that is true yet. Weare interested in finding out the link,” she said.
41. According to the passage, when stress affects human beings, what tissue can show the effect from the outside?
(A) muscular tissue
(B) eyebrow
(C) skin
(D) nervous tissue