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: Development of ocular myasthenia during pegylated interferon and ribavirin treatment for chronic hepatitis C .
### Output Text:
Development of ocular myasthenia during <span class="chemical">pegylated interferon</span> and <span class="chemical">ribavirin</span> treatment for chronic hepatitis C . 