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: Among relatively healthy women over 65 years taking continuous combined HT , there was a statistically significant increase in the incidence of dementia .
### Output Text:
Among relatively healthy women over 65 years taking continuous combined HT , there was a statistically significant increase in the incidence of dementia . 