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: We need more evidence on the safety of HT for menopausal symptom control , though short - term use appears to be relatively safe for healthy younger women .
### Output Text:
We need more evidence on the safety of HT for menopausal symptom control , though short - term use appears to be relatively safe for healthy younger women . 