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: ATT - ALF patients were younger ( 32 . 87 [ + / - 15 . 8 ] years ) , and 49 ( 70 % ) of them were women .
### Output Text:
ATT - ALF patients were younger ( 32 . 87 [ + / - 15 . 8 ] years ) , and 49 ( 70 % ) of them were women . 