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: Controls were patients admitted to the same hospitals from where the cases arose , also matched by age and sex .
### Output Text:
Controls were patients admitted to the same hospitals from where the cases arose , also matched by age and sex . 