Ethiopians appear to have evolved a
unique way of coping with thin mountain air. But how they do it remains a
mystery. One way for the body to get enough oxygen to its tissues when breathing oxygen-poor air is for it to make more red blood cells. This increases the amount of hemoglobin(血红蛋白), the protein that carries oxygen. Although less haemoglobin in the arteries is saturated with oxygen at high altitudes, having more of it makes up for the shortfall. People native to the high Andes are known to have more red blood cells than lowlanders, and athletes who train at altitude can increase their concentration of cells. But while many Tibetans also live at high altitudes, they do not have significantly elevated levels of haemoglobin. Instead they seem to boost the amount of nitric oxide, which dilates(使膨胀) blood vessels and A. oxygen B. blood cell C. protein D. artery [填空题]How can you protect other people when you have a cold
______ with a tissue when you cough or sneeze at least. [填空题]Unless children have other people in their lives who speak another language, they won’t become fluent speakers in that language.
[填空题]People have always tried to "type" each other. Actors in early Greek drama wore masks to show the audience whether they played the villain’s (坏人) or the hero’s role. In fact, the words "person" and "personality" come from the Latin persona, meaning" mask. "Today, most television and movie actors do not wear masks ______.
[填空题]People can have meals there.
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