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: Five females and 6 males , 21 - 59 years of age , were examined with a 1 . 5 - T whole - body system using a circular polarized head coil .
### Output Text:
Five females and 6 males , 21 - 59 years of age , were examined with a 1 . 5 - T whole - body system using a circular polarized head coil . 