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: Mice in the early stage of LP - BM5 MuLV disease were given AZT in their drinking water at 1 . 0 and 2 . 5 mg / ml .
### Output Text:
Mice in the early stage of LP - BM5 MuLV disease were given <span class="chemical">AZT</span> in their drinking water at 1 . 0 and 2 . 5 mg / ml . 