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: Fifteen polydrug ecstasy users and 15 polydrug non - ecstasy user controls completed a general drug use questionnaire , the Brixton Spatial Anticipation task ( set shifting ) , Backward Digit Span procedure ( memory updating ) , Inhibition of Return ( inhibition ) , an emotional intelligence scale , the Tromso Social Intelligence Scale and the Dysexecutive Questionnaire ( DEX ) .
### Output Text:
Fifteen polydrug <span class="chemical">ecstasy</span> users and 15 polydrug non - <span class="chemical">ecstasy</span> user controls completed a general drug use questionnaire , the Brixton Spatial Anticipation task ( set shifting ) , Backward Digit Span procedure ( memory updating ) , Inhibition of Return ( inhibition ) , an emotional intelligence scale , the Tromso Social Intelligence Scale and the Dysexecutive Questionnaire ( DEX ) . 