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: Cystic hyperplasia was associated with unopposed oestrogen therapy without progestagen .
### Output Text:
Cystic hyperplasia was associated with unopposed <span class="chemical">oestrogen</span> therapy without <span class="chemical">progestagen</span> . 