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: NX + HP caused a further rise in blood pressure in Li - pretreated rats .
### Output Text:
NX + HP caused a further rise in blood pressure in <span class="chemical">Li</span> - pretreated rats . 