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: In normal rats , 2 / 6 rats given free doxorubicin ( DX ) ( 5 mg / kg ) died within one week , whereas all control animals and all rats having received free NP or DXNP survived .
### Output Text:
In normal rats , 2 / 6 rats given free <span class="chemical">doxorubicin</span> ( <span class="chemical">DX</span> ) ( 5 mg / kg ) died within one week , whereas all control animals and all rats having received free NP or DXNP survived . 