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: Total ASEX scores were significantly lower , i . e . better , among men who received bupropion than placebo , at 15 . 5 ( 4 . 3 ) vs 21 . 5 ( 4 . 7 ) ( P = 0 . 002 ) .
### Output Text:
Total ASEX scores were significantly lower , i . e . better , among men who received <span class="chemical">bupropion</span> than placebo , at 15 . 5 ( 4 . 3 ) vs 21 . 5 ( 4 . 7 ) ( P = 0 . 002 ) . 