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: Potential therapeutic use of the selective dopamine D1 receptor agonist , A - 86929 : an acute study in parkinsonian levodopa - primed monkeys .
### Output Text:
Potential therapeutic use of the selective <span class="chemical">dopamine</span> D1 receptor agonist , <span class="chemical">A - 86929</span> : an acute study in parkinsonian <span class="chemical">levodopa</span> - primed monkeys . 