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: CONCLUSION : During dobutamine stress testing , metoprolol attenuates or eliminates evidence of myocardial ischemia .
### Output Text:
CONCLUSION : During <span class="chemical">dobutamine</span> stress testing , <span class="chemical">metoprolol</span> attenuates or eliminates evidence of myocardial ischemia . 