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: Dosage groups of 15 , 30 , 50 , 75 , 100 , 125 , 150 , 175 or 200 microg carbetocin were assigned to blocks of three women according to the continual reassessment method ( CRM ) .
### Output Text:
Dosage groups of 15 , 30 , 50 , 75 , 100 , 125 , 150 , 175 or 200 microg <span class="chemical">carbetocin</span> were assigned to blocks of three women according to the continual reassessment method ( CRM ) . 