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: DATA SYNTHESIS : New evidence from 1 good - quality RCT , 1 good - quality meta - analysis , and 2 fair - quality subanalyses of RCTs demonstrates that aspirin use reduces the number of CVD events in patients without known CVD .
### Output Text:
DATA SYNTHESIS : New evidence from 1 good - quality RCT , 1 good - quality meta - analysis , and 2 fair - quality subanalyses of RCTs demonstrates that <span class="chemical">aspirin</span> use reduces the number of CVD events in patients without known CVD . 