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: This case emphasizes the possibility that HUS in adults is not invariably irreversible and that , despite prolonged oliguria , recovery of renal function can be obtained .
### Output Text:
This case emphasizes the possibility that HUS in adults is not invariably irreversible and that , despite prolonged oliguria , recovery of renal function can be obtained . 