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Strikingly , although V - 3 and V - 4 had opposite effects on MRP2 activity , they are structurally identical except for their chalcogen atom ( Se versus Te ) .
 chalcogen, Se, Te
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 chalcogen, Se, Te