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 20 - year risk of CAD at diagnosis of diabetes , using the UKPDS risk engine , was used to match cases with controls .
### Output Text:
The 20 - year risk of CAD at diagnosis of diabetes , using the UKPDS risk engine , was used to match cases with controls . 