问题
选择题
下列各组物质中，互为同位素的是[ ]
A．氕和氘
B．甲烷和乙烷
C．金刚石和石墨
D．丁烷和异丁烷
答案
答案：A
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下列各组物质中，互为同位素的是[ ]
A．氕和氘
B．甲烷和乙烷
C．金刚石和石墨
D．丁烷和异丁烷
答案：A
Somebody says ,‘‘Time is money.” But I think time is important than money. Why do I think so? Because when money is over, we can get it back. But when time is it’ll never .That’s we shouldn’t waste time. It goes with saying that the is usually limited. Even a second is very important .We should make full use of our time to do useful. But a lot of people do not know the importance of time. It is a pity. They spend their limited time smoking, drinking, sleeping and . They do not know that wasting time means wasting part of their own . In a word, we should save time. We shouldn’t today’s work for tomorrow. Please remember that we have no time to .
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