某非金属元素的原子核外最外层电子数是次外层电子数的一半，该元素：
A．在自然界中只以化合态的形式存在
B．单质常用作半导体材料和光导纤维
C．最高价氧化物不与酸反应
D．常温下与氯气反应
答案：A
该元素为2、1或2、8、4结构，为Li或Si；又因为为非金属，故只有Si符合；A、硅为亲氧元素，故只以化合态存在；B、光导纤维为二氧化硅；C、二氧化硅与HF反应；D、硅常温下不与氯气反应。
Mary is an American schoolgirl. 小题1: . She doesn’t know Chinese, but she is trying to study and speak it. 小题2: . Sometimes they don’t understand her, because she can’t speak Chinese well.It’s Saturday morning. Mary goes out. She is on her way to the park. She is going there to see a flower show（展览）. 小题3: . She asks a Chinese boy. The boy can’t understand her. 小题4: . She draws flowers on it, gives the picture to the boy and says something about it. The boy smiles and then shows Mary the way to the park
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