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: OBJECTIVE : To describe 3 patients with calcium carbonate - induced hypercalcemia and gain insights into the cause and management of the milk - alkali syndrome .
### Output Text:
OBJECTIVE : To describe 3 patients with <span class="chemical">calcium carbonate</span> - induced hypercalcemia and gain insights into the cause and management of the milk - alkali syndrome . 