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: Due to the interdependence of risk factors in clinical populations , it is difficult to independently examine factors that may influence the development of LIDs .
### Output Text:
Due to the interdependence of risk factors in clinical populations , it is difficult to independently examine factors that may influence the development of LIDs . 