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: The study included 871 women with HIV who were recruited from 1993 - 1995 in four US cities .
### Output Text:
The study included 871 women with HIV who were recruited from 1993 - 1995 in four US cities . 