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: Benzylacyclouridine reverses azidothymidine - induced marrow suppression without impairment of anti - human immunodeficiency virus activity .
### Output Text:
<span class="chemical">Benzylacyclouridine</span> reverses <span class="chemical">azidothymidine</span> - induced marrow suppression without impairment of anti - human immunodeficiency virus activity . 