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: DNA SBs damage was negatively associated with TAP ( R = - 0 . 98 , p = 0 . 018 ) , and necrosis ( R = - 0 . 97 , p = 0 . 027 ) .
### Output Text:
DNA SBs damage was negatively associated with TAP ( R = - 0 . 98 , p = 0 . 018 ) , and necrosis ( R = - 0 . 97 , p = 0 . 027 ) . 