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: Untreated group 3 rats exhibited a progressive reduction in GFR ( 0 . 35 + / - 0 . 08 ml / min at 4 months , 0 . 27 + / - 0 . 07 ml / min at 6 months ) .
### Output Text:
Untreated group 3 rats exhibited a progressive reduction in GFR ( 0 . 35 + / - 0 . 08 ml / min at 4 months , 0 . 27 + / - 0 . 07 ml / min at 6 months ) . 