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: Monitoring of serum calcium and cis - RA levels is indicated in future trials .
### Output Text:
Monitoring of serum <span class="chemical">calcium</span> and <span class="chemical">cis - RA</span> levels is indicated in future trials . 