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: One hundred and thirty - five patients were assigned to one of three groups in a prospective , double blind , randomized manner .
### Output Text:
One hundred and thirty - five patients were assigned to one of three groups in a prospective , double blind , randomized manner . 