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In the last few years delayed reactions several hours after the injection of radiographic and contrast materials ( PRC ) have been described with increasing frequency .
 Chemical: contrast materials; Chemical: PRC
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Disease, Chemical 
Text: {0} 
Answer:
 Chemical: contrast materials; Chemical: PRC