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阅读理解     It's undeniable that spending time outdoors and in nature lifts our spirits and makes us feel more centered and at peace. When we breathe in fresh air, and enjoy the beauty of trees, streams and oceans, we naturally tend to feel more connected to ourselves and others. Over the past decade, scientists have been exploring why nature — and dirt specifically — is such a powerful tool in improving our mood. According to researchers, the secret may lie in the microbes (微生物)of the soil. One bacterium specifically—-Mycobacterium Vaccae (M. Vaccae) —has been identified as having the power to affect our moods and cognitive function as well.     Experiments conducted at Sage Colleges in New York found that contact with M. Vaccae can increase serotonin levels in the brain — a chemical that is associated with higher levels of happiness, increased focus, and reduced anxiety. In order to explore how the bacteria can improve learning, researchers Dory Mathews and Susan Jenks experimented with mice in a maze. Mice that ingested the bacteria navigated the maze twice as fast as the control group and proved less anxious as well.     Humans can absorb M. Vaccae just by playing in the dirt. We take in it when we breathe, we consume it in organic vegetables, and it can also enter our bloodstream through skin contact, especially where we have open cuts. This may explain why children in school perform better after break.     Neuroscientist Christopher Lowry at the University of Bristol in England believes that he has identified why this incredible bacterium works. "What we think happens is that the bacteria activate immune cells, which release chemicals called cytokines that then act on receptors on the sensory nerves to increase their activity.”     Beyond the power of M. Vaceae, scientists have been proving for decades that exposure to dirt, and the huge number of microbes found in dirt, can strengthen our immune system. When our body comes into contact with bacteria, it stores die information in a type of library and can then use that information to fight sickness and infection more effectively.     Happiness, focus, less anxiety… I'll take a double dose of dirt; please! （1） What raises people's spirits while spending time outdoors? A . Air. B . Trees. C . Water D . Dirt. （2） How does M. Vaccae work? A . By working on sensory nerves. B . By fighting sickness and infection. C . By strengthening the immune system. D . By making immune cells active. （3） According to the text, what does the author intend to do next? A . Provide some advice on reducing anxiety for readers, B . Summarize the previous paragraphs about lifting one's mood. C . Explain how he or she will expose himself or herself to dirt. D . Introduce a new topic related to dirt for discussion. （4） What can be a suitable title for the text? A . Fight Sickness and Infection More Effectively B . How Getting Dirty Can Actually lift Your Mood C . Let's Take a Deep Breath of Fresh Air D . Enjoy Beauty and Naturally Connect to Others 答案： D D C B

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