有关原子的叙述正确的是（ ）
A．原子都是由质子和电子构成的
B．原子中质子数不一定等于电子数
C．原子中一定含有中子
D．原子是由原子核和核外电子构成的
因为原子由原子核和核外电子构成，其中原子核由质子和中子构成的，则可知正确答案．
A、原子由原子核和核外电子构成，质子数一定等于电子数，叙述错误
B、原子由原子核和中子构成，叙述错误，应原子核和电子，错误；
C、原子中不一定含有中子，例如氢原子，故错误．
D、原子由原子核和核外电子构成，其中原子核由质子和中子构成的，故正确．
故选D．
Is global warming killing the Maldives? The Maldives(马尔代夫) is one of the most beautiful countries in the world. Every year, millions of go there to enjoy the wonderful scenery. And in recent years, more and more people would like to visit it, ? Because the little island country is . If global warming , say scientists, the country will go down into the ocean within 100 years. That means the Maldives have disappeared by 2100. The Maldives in the Indian Ocean. It is the country on earth—its highest point is only 2.4m above sea level. Greenhouse gas emissions（排放）, global temperature and sea levels will rise 9cm and 88cm by 2100. If scientists are , most of the Maldives will be covered with water in years. Last October, Maldivian President Mohamed Nasheed and his cabinet（内阁）held the world’s first underwater cabinet meeting to make the world the terrible results from global warming to their own country. In December, he at the 2009 United Nations Climate Change Conference（大会） in Copenhagen, trying to ask for help from the world for country. The president even has a to buy a new homeland and move his country and people to a new place. The Moldavian government has been doing all it can to fight the . But the fate（命运）of the islands is in the world’s hands. No one wants to see this little island country disappear from the world.
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