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: Women were randomised to receive tamoxifen 20 mg per day or placebo , both orally for 5 years .
### Output Text:
Women were randomised to receive <span class="chemical">tamoxifen</span> 20 mg per day or placebo , both orally for 5 years . 