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: We sought to confirm this correlation with and without adjustment for prognostic variables and to investigate outcome in subgroups with increasing levels of BP reduction .
### Output Text:
We sought to confirm this correlation with and without adjustment for prognostic variables and to investigate outcome in subgroups with increasing levels of BP reduction . 