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: Positive test results were more common in patient visits where there was a history or suspicion of cocaine or amphetamine abuse ( p < 0 . 0005 ) .
### Output Text:
Positive test results were more common in patient visits where there was a history or suspicion of cocaine or amphetamine abuse ( p < 0 . 0005 ) . 