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: Myoclonus associated with lorazepam therapy in very - low - birth - weight infants .
### Output Text:
Myoclonus associated with <span class="chemical">lorazepam</span> therapy in very - low - birth - weight infants . 