The Caribbean Islands form a chain that separates the Caribbean Sea from the rest of the Atlantic Ocean. ________. Many of the islands were formed by the eruption（爆发）of ancient volcanoes（火山）．Others are low-lying coral islands that gradually rose from the ocean.
A、They are famous for their warm, tropical climate and great natural beauty.
B、What would you see if you took a cruise to the Caribbean Islands?
C、They're like a long necklace that stretches between North and South America.
D、But life on the Caribbean Islands is not always paradise.
【答案解析】 第一句话说的是：加勒比群岛形成了一个锁链，把加勒比海与大西洋的其他部分分开。答案是C，因为它的第一个词是"They"，该词指"The Caribbean Islands"；而且在语义上也有很好的衔接。