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: Scleroderma renal crisis ( SRC ) is a rare complication of systemic sclerosis ( SSc ) but can be severe enough to require temporary or permanent renal replacement therapy .
### Output Text:
Scleroderma renal crisis ( SRC ) is a rare complication of systemic sclerosis ( SSc ) but can be severe enough to require temporary or permanent renal replacement therapy . 