1. A 词义猜测题。根据They are classified as carcinogens by the International Agency for Research on Cancer. 可知这个词与癌症有关，故可推出carcinogenic意为"致癌的"。

2. C 细节题。根据People found the dye in 1883 and gave it the name. Nobody knows the reason, and we cannot give any explanation before we find out.可知还没有人知道"苏丹红"名称的由来。

3. B 推断题。根据EU officials have been striving to remove some food products from the shelves. So far 580 products have been recalled.可知某些食品因含有"苏丹红"而被召回。故可推断"苏丹红"经常用作食品添加剂。

4. B 主旨大意题。根据there has been confusion over possible links to the country of the same name, but Sudan officials say there is no connection whatever. 可知本文主要讲"苏丹红"与苏丹这个国家是否有联系的问题，故B最佳。