问题
选择题
镁不但能在空气中燃烧，也能在二氧化碳气体中燃烧。下列说法错误的是[ ]
A．燃烧一定要有氧气参加
B．燃烧反应都属于氧化反应
C．镁等活泼金属着火不能用二氧化碳来灭火
D．镁在空气、二氧化碳气体中燃烧都是放热反应
答案
答案：A
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镁不但能在空气中燃烧，也能在二氧化碳气体中燃烧。下列说法错误的是[ ]
A．燃烧一定要有氧气参加
B．燃烧反应都属于氧化反应
C．镁等活泼金属着火不能用二氧化碳来灭火
D．镁在空气、二氧化碳气体中燃烧都是放热反应
答案：A
Recently, researchers in the US have carried out a study on laughing, one of the most natural characteristics of human behavior. Jo-Anne Bachorowsky, a psychology professor at Vandebilt University, 36 a team of researchers who 37 a total of 11 short videos to 97 young adult volunteers in the US. They found that the participants produced a 38 of sounds when they laughed, 39 grunts(呼噜声) and snorts(哼声). The researchers found that some of the 40 were dependent 41 gender(性别). Men laughed with grunts and snorts more often than women, 42 women’s 43 was more song-like. They also found that people’s laughter could change, 44 who they were with at the time. Whether they were with a man or a woman and 45 person was a friend or a 46 both played a part in laughter. The researchers found that women’s laughter was very high with a 47 pitch(音高) when they were with male strangers. And women taking 48 in the study laughed more often when they were with a male friend than when they were with a(n) 49 friend or a male stranger. But men laughed more freely with friends of either sex than with strangers of either sex. Scientists believe that the 50 consumed in laughing 100 times is 51 to 15 minutes on an exercise bike. Another 52 of laughter is 53 it improves our mental health. Laughter reduces our levels of stress. It also helps us 54 serious illness. 55 ,we think laughter can make us feel good.
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