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: Male F344 rats , 5 weeks of age , were maintained on diet containing 1 % or 2 % BHA by weight and simultaneously on drinking water supplemented with RA at various concentrations ( w / v ) for 52 weeks .
### Output Text:
Male F344 rats , 5 weeks of age , were maintained on diet containing 1 % or 2 % <span class="chemical">BHA</span> by weight and simultaneously on drinking water supplemented with <span class="chemical">RA</span> at various concentrations ( w / v ) for 52 weeks . 