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: This difference was also significant in the primary valve surgery and the high risk surgery subgroups ( 7 . 9 % vs 1 . 2 % , P = 0 . 003 ; 7 . 3 % vs 2 . 4 % , P = 0 . 035 , respectively ) .
### Output Text:
This difference was also significant in the primary valve surgery and the high risk surgery subgroups ( 7 . 9 % vs 1 . 2 % , P = 0 . 003 ; 7 . 3 % vs 2 . 4 % , P = 0 . 035 , respectively ) . 