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: Fourteen weeks after the start of phosphate supplementation , half of the Nx and Sham dogs received doses of OCT ( three times per week ) ; the other half were given vehicle for 60 weeks .
### Output Text:
Fourteen weeks after the start of <span class="chemical">phosphate</span> supplementation , half of the Nx and Sham dogs received doses of <span class="chemical">OCT</span> ( three times per week ) ; the other half were given vehicle for 60 weeks . 