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: The data may indicate that although D - 2 receptor blockade is involved in catalepsy , the D - 1 receptor may plan a role .
### Output Text:
The data may indicate that although D - 2 receptor blockade is involved in catalepsy , the D - 1 receptor may plan a role . 