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: In status epilepticus ( P20 ) rats , acquisition of the sound - source location discrimination was moderately impaired .
### Output Text:
In status epilepticus ( P20 ) rats , acquisition of the sound - source location discrimination was moderately impaired . 