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: All four agents were associated with aortic arch branching variants , although significantly increased only for Ro 40 - 5967 and verapamil .
### Output Text:
All four agents were associated with aortic arch branching variants , although significantly increased only for <span class="chemical">Ro 40 - 5967</span> and <span class="chemical">verapamil</span> . 