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: RESULTS : After 12 weeks of treatment , the mean ( sd ) scores for CGI - SF were significantly lower , i . e . better , in patients on bupropion SR , at 2 . 4 ( 1 . 2 ) , than in the placebo group , at 3 . 9 ( 1 . 1 ) ( P = 0 . 01 ) .
### Output Text:
RESULTS : After 12 weeks of treatment , the mean ( sd ) scores for CGI - SF were significantly lower , i . e . better , in patients on <span class="chemical">bupropion</span> SR , at 2 . 4 ( 1 . 2 ) , than in the placebo group , at 3 . 9 ( 1 . 1 ) ( P = 0 . 01 ) . 