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: Thirty - six rats bearing breast tumors induced chemically were divided into 4 groups : control , hydroxytyrosol ( 0 . 5mg / kg , 5days / week ) , doxorubicin ( 1mg / kg / week ) , and doxorubicin plus hydroxytyrosol .
### Output Text:
Thirty - six rats bearing breast tumors induced chemically were divided into 4 groups : control , <span class="chemical">hydroxytyrosol</span> ( 0 . 5mg / kg , 5days / week ) , <span class="chemical">doxorubicin</span> ( 1mg / kg / week ) , and <span class="chemical">doxorubicin</span> plus <span class="chemical">hydroxytyrosol</span> . 