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: BACKGROUND : A 72 - year - old white man with underlying human immunodeficiency virus , atrial fibrillation , coronary artery disease , and hyperlipidemia presented with generalized pain , fatigue , and dark orange urine for 3 days .
### Output Text:
BACKGROUND : A 72 - year - old white man with underlying human immunodeficiency virus , atrial fibrillation , coronary artery disease , and hyperlipidemia presented with generalized pain , fatigue , and dark orange urine for 3 days . 