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: In Nx dogs , OCT reversed abnormal bone formation , such as woven osteoid and fibrosis , but did not significantly alter the level of bone turnover .
### Output Text:
In Nx dogs , <span class="chemical">OCT</span> reversed abnormal bone formation , such as woven osteoid and fibrosis , but did not significantly alter the level of bone turnover . 