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 the hypertensive group ( n = 7 ) , the MAP was elevated by 25 - 30 mm Hg beginning 2 h after MCAO .
### Output Text:
In the hypertensive group ( n = 7 ) , the MAP was elevated by 25 - 30 mm Hg beginning 2 h after MCAO . 