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: Rats were divided into three groups : sham , VCM and VCM plus erdosteine .
### Output Text:
Rats were divided into three groups : sham , <span class="chemical">VCM</span> and <span class="chemical">VCM</span> plus <span class="chemical">erdosteine</span> . 