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: It was hypothesized that progestins could equilibrate the effects of the estrogenic stimulation on the mammary and endometrial target tissues of women on hormonal replacement therapy .
### Output Text:
It was hypothesized that <span class="chemical">progestins</span> could equilibrate the effects of the estrogenic stimulation on the mammary and endometrial target tissues of women on hormonal replacement therapy . 