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: Prolonged administration of female sex hormones is a possible cause of chorea in women who have not previously had chorea or rheumatic fever .
### Output Text:
Prolonged administration of female sex hormones is a possible cause of chorea in women who have not previously had chorea or rheumatic fever . 