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: CPA reduced cocaine action at the doses which , given alone , did not influence motility , while CGS 21680 and NECA decreased the action of cocaine at the doses which , given alone , decreased locomotor activity in animals .
### Output Text:
<span class="chemical">CPA</span> reduced <span class="chemical">cocaine</span> action at the doses which , given alone , did not influence motility , while <span class="chemical">CGS 21680</span> and <span class="chemical">NECA</span> decreased the action of <span class="chemical">cocaine</span> at the doses which , given alone , decreased locomotor activity in animals . 