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: The levels of cholesterol , triglyceride and LDL in blood of rats were analyzed .
### Output Text:
The levels of <span class="chemical">cholesterol</span> , <span class="chemical">triglyceride</span> and LDL in blood of rats were analyzed . 