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: Consequently , whereas all participants exhibited normotensive levels during the resting predrug baseline , 33 % of borderline subjects achieved hypertensive BP levels after caffeine ingestion .
### Output Text:
Consequently , whereas all participants exhibited normotensive levels during the resting predrug baseline , 33 % of borderline subjects achieved hypertensive BP levels after <span class="chemical">caffeine</span> ingestion . 