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: Risk in the raloxifene group was higher than in the placebo group for the first 2 years , but decreased to about the same rate as in the placebo group thereafter .
### Output Text:
Risk in the <span class="chemical">raloxifene</span> group was higher than in the placebo group for the first 2 years , but decreased to about the same rate as in the placebo group thereafter . 