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: SELECTION CRITERIA : Randomised double - blind trials of HT ( oestrogens with or without progestogens ) versus placebo , taken for at least one year by perimenopausal or postmenopausal women .
### Output Text:
SELECTION CRITERIA : Randomised double - blind trials of HT ( <span class="chemical">oestrogens</span> with or without <span class="chemical">progestogens</span> ) versus placebo , taken for at least one year by perimenopausal or postmenopausal women . 