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: Group 1 ( P alone ) received P , 360 mg / day , for 15 days ; Group II ( P + gentamicin ) ; Group III ( gentamicin alone ) and Group IV ( mild DM + gentamicin ) .
### Output Text:
Group 1 ( <span class="chemical">P</span> alone ) received <span class="chemical">P</span> , 360 mg / day , for 15 days ; Group II ( <span class="chemical">P</span> + <span class="chemical">gentamicin</span> ) ; Group III ( <span class="chemical">gentamicin</span> alone ) and Group IV ( mild DM + <span class="chemical">gentamicin</span> ) . 