A. It states the main idea of the paragraph. B. It supports the main idea by providing a reason. C. It states an idea that is in contrast to the main idea. D. It supports the main idea by providing an example. 参考答案:D 答案解析:该题问的是段落中一句话在文中的作用,既测试对语句的理解,也检测对篇章结构的掌握。“Sulfur is one of those elements.”根据上下文信息,可以判断出这句话的作用在于举例说明。