请阅读下面这篇文章，根据所提供的信息，回答5个问题。要求所写答案语法正确、语义完整，并将答题卡上对应题目所选的选项涂黑。Do you like a small plant? The study shows that a small plant can improve our memory (记忆力) and make us happier. Even the small plants on your desk may have a more effect on you than you might realize. The small plants can help you to think more clearly. Studies have shown that the small plants could improve your concentration (注意力) by up to 20% and improve your ability to remember information by 15-20%. Plants can also reduce CO2 and improve air quality.
"CO2 should not pass 1,000 parts per million in the classroom." Doctor Zhang in the Health and Safety Center said. He said this level can cause headache and even lead to poorer decision-making. Studies have shown that sometimes indoors plants can reduce CO2 from 2,000ppm to about 480ppm in less than one hour. Plants can increase happiness because there is endorphins (内啡肽) in humans. The shape, color, smell, feel and taste of plants can cheer us up and improve our memories.
