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: BACKGROUND : The mechanisms underlying heart failure induced by adriamycin are very complicated and still unclear .
### Output Text:
BACKGROUND : The mechanisms underlying heart failure induced by <span class="chemical">adriamycin</span> are very complicated and still unclear . 