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: A possible association between steroid therapy and subsequent postinfarction septal rupture is discussed .
### Output Text:
A possible association between <span class="chemical">steroid</span> therapy and subsequent postinfarction septal rupture is discussed . 