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: Lamivudine is effective in suppressing hepatitis B virus DNA in Chinese hepatitis B surface antigen carriers : a placebo - controlled trial .
### Output Text:
<span class="chemical">Lamivudine</span> is effective in suppressing hepatitis B virus DNA in Chinese <span class="chemical">hepatitis B surface antigen</span> carriers : a placebo - controlled trial . 