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: RESULTS : While the CAN and PD groups tended to record greater deficits than the non - drug controls , the MDMA and EX - MDMA groups recorded greater deficits than all the control groups on ten of the 13 psychometric measures .
### Output Text:
RESULTS : While the <span class="chemical">CAN</span> and PD groups tended to record greater deficits than the non - drug controls , the <span class="chemical">MDMA</span> and EX - <span class="chemical">MDMA</span> groups recorded greater deficits than all the control groups on ten of the 13 psychometric measures . 