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: Neurologic status returned to baseline within 10 days of the acute event , and magnetic resonance angiography findings returned to normal 4 months later .
### Output Text:
Neurologic status returned to baseline within 10 days of the acute event , and magnetic resonance angiography findings returned to normal 4 months later . 