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: The 80 patients in the study consecutively received either iopromide ( group A , n = 40 ) or iohexol ( group B , n = 40 ) .
### Output Text:
The 80 patients in the study consecutively received either <span class="chemical">iopromide</span> ( group A , n = 40 ) or <span class="chemical">iohexol</span> ( group B , n = 40 ) . 