In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: CONCLUSION : The magnitude of the association with PPH , the increase of association with increasing duration of use , and the specificity for fenfluramines are consistent with previous studies indicating that fenfluramines are causally related to PPH .
### Output Text:
CONCLUSION : The magnitude of the association with PPH , the increase of association with increasing duration of use , and the specificity for <span class="chemical">fenfluramines</span> are consistent with previous studies indicating that <span class="chemical">fenfluramines</span> are causally related to PPH . 