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: 17beta - Estradiol reduced the argyrophilic neurons in the CA1 and CA3 - C sectors of ovariectomized rats .
### Output Text:
<span class="chemical">17beta - Estradiol</span> reduced the argyrophilic neurons in the CA1 and CA3 - C sectors of ovariectomized rats . 