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: For this purpose , bile salt pool composition , synthesis of individual BS in vivo , hepatic activities , and expression levels of cholesterol 7alpha - hydroxylase ( CYP7A ) , and sterol 27 - hydroxylase ( CYP27 ) , as well as of other enzymes involved in BS synthesis , were analyzed in rats treated with EE ( 5 mg / kg , 3 days ) or its vehicle .
### Output Text:
For this purpose , <span class="chemical">bile salt</span> pool composition , synthesis of individual <span class="chemical">BS</span> in vivo , hepatic activities , and expression levels of <span class="chemical">cholesterol</span> 7alpha - hydroxylase ( CYP7A ) , and <span class="chemical">sterol</span> 27 - hydroxylase ( CYP27 ) , as well as of other enzymes involved in <span class="chemical">BS</span> synthesis , were analyzed in rats treated with <span class="chemical">EE</span> ( 5 mg / kg , 3 days ) or its vehicle . 