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: Groups of male and female inbred Leeds strain rats were fed diets containing either 0 . 5 % or 1 . 0 % paracetamol by weight for up to 18 months .
### Output Text:
Groups of male and female inbred Leeds strain rats were fed diets containing either 0 . 5 % or 1 . 0 % <span class="chemical">paracetamol</span> by weight for up to 18 months . 