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: BS pool size was decreased by 27 % but total BS synthesis was not affected by EE in intact rats .
### Output Text:
<span class="chemical">BS</span> pool size was decreased by 27 % but total <span class="chemical">BS</span> synthesis was not affected by <span class="chemical">EE</span> in intact rats . 