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: Liver LPO levels were not elevated until day 7 of treatment ( 1 . 8 - fold versus control , p < 0 . 05 ) .
### Output Text:
Liver <span class="chemical">LPO</span> levels were not elevated until day 7 of treatment ( 1 . 8 - fold versus control , p < 0 . 05 ) . 