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: In contrast , although the chlorpheniramine group did have fewer symptoms than the placebo group during the study , the difference never reached statistical significance during any week of the study .
### Output Text:
In contrast , although the <span class="chemical">chlorpheniramine</span> group did have fewer symptoms than the placebo group during the study , the difference never reached statistical significance during any week of the study . 